JP7296938B2 - Method and apparatus for performing random access procedure - Google Patents

Description

TECHNICAL FIELD The present invention relates to a system, method, and apparatus for performing random access procedures in a wireless communication system, and more specifically, the present invention provides a PRACH preamble and/or PRACH resource/occasion during a random access procedure. Regarding how to choose.

Efforts are being made to develop improved 5G communication systems or pre-5G communication systems to meet the growing need for wireless data traffic after the commercialization of 4G communication systems.
For this reason, 5G communication systems or pre-5G communication systems are called Beyond 4G Network communication systems or Post LTE systems.

In order to achieve high data transmission rates, 5G communication systems are being considered for implementation in ultra-high frequency (mmWave) bands (eg, such as the 60 Giga (60 GHz) band).
In order to alleviate the path loss of radio waves in the ultra-high frequency band and increase the transmission distance of radio waves, 5G communication systems use beamforming, massive MIMO (multiple-input and multiple-output), Full Dimensional MIMO (FD-MIMO), array antenna, analog beam-forming, and large scale antenna techniques are discussed.

In addition, for the network improvement of the system, the 5G communication system has evolved small cells, advanced small cells, cloud radio access network (cloud RAN), ultra-high density network (ultra- dense network), device to device communication (D2D), wireless backhaul, moving network, cooperative communication, CoMP (Coordinated Multi-Point ts), and received interference Techniques such as interference cancellation have been developed.

In addition, in the 5G system, FQAM (Hybrid FSK and QAM Modulation) and SWSC (Sliding Window Super position Coding), which are advanced coding modulation (ACM) methods, and FBMC (Filter Bank Multi Carrier), NOMA (non-orthogonal multiple access), and SCMA (sparse code multiple access) have been developed.

On the other hand, the Internet is evolving from a human-centered connection network in which humans generate and consume information to an IoT (Internet of Things) network in which information is exchanged and processed among distributed components such as things. be.
Internet of Everything (IoE) technology, in which IoT technology is combined with big data processing technology through connection with cloud servers, is also emerging.
In order to implement IoT, technology elements such as sensing technology, wired/wireless communication, network infrastructure, service interface technology, and security technology are required. Techniques such as machine-to-machine (M2M) and MTC (Machine Type Communication) are being studied.

In the IoT environment, intelligent IT (Internet Technology) services that create new value in human life by collecting and analyzing data generated by connected things can be provided.
Through the integration and combination of existing IT technology and various industries, IoT is expanding into fields such as smart homes, smart buildings, smart cities, smart cars or connected cars, smart grids, healthcare, smart home appliances, and advanced medical services. can be applied.

Various attempts have been made to apply the 5G communication system to the IoT network.
For example, technologies such as sensor networks, machine to machine (M2M), MTC (Machine Type Communication), and 5G communication technologies are implemented by techniques such as beamforming, MIMO, and array antennas. It is that you are.
The application of the cloud radio access network (cloud RAN) as the aforementioned big data processing technology is also an example of the fusion of 5G technology and IoT technology.

In recent years, many broadband wireless technologies have been developed to accommodate the growing number of broadband subscribers and to provide more and better applications and services.
Second generation (2G) wireless communication systems have been developed to provide voice services while ensuring user mobility.
Third generation (3G) wireless communication systems support data services as well as voice services.
4G wireless communication systems have been developed to provide high speed data services.
However, 4G wireless communication systems are currently running out of resources to meet the increasing demand for high speed data services.
Therefore, 5G wireless communication systems are being developed to meet the increasing demand for high speed data services, ultra-reliability and low latency applications.

Furthermore, 5G wireless communication systems are expected to handle different use cases with very different requirements in terms of data rate, latency, reliability, mobility, and so on.
However, the design of the air interface of the 5G wireless communication system serves user equipment (UE) with very different capabilities depending on the use case, and the UE cater service to the end customer market segment. It is expected to be flexible enough to (market segment).
Exemplary use cases expected to be handled by 5G wireless communication systems are eMBB (enhanced mobile broadband), m-MTC (massive machine type communication), URLL (ultra-reliable low latency communication), and so on.

eMBB requirements such as data speeds in the tens of Gbps, low latency, high mobility, etc. are driving existing wireless broadband subscribers who need Internet connectivity everywhere, all the time and on the go. deals with market segments that represent
m-MTC requirements such as very high connection density, rare data TX, very long battery life, low mobility address, etc. are driving the market segment to point to IoT/IoE assuming connectivity of billions of devices. deal.
URLL requirements such as very low latency, very high reliability, and variable mobility are predicted as one of the things that can be done for industrial automation applications, autonomous vehicles. It deals with market segments representing vehicle-to-vehicle/vehicle-to-infrastructure communications.

In an existing wireless communication system, namely LTE, a random access (RA) procedure is used to achieve uplink time synchronization.
RA procedures include initial access, handover, radio resource control (RRC) connection reconfiguration procedure, positioning purpose, scheduling request transmission, SCG (secondary cell group) addition/modification, and RRC CONNECTED state. is used in LTE during data or control information transmission on the uplink by a desynchronized UE.
Two types of RA procedures are defined in LTE: 'contention-based' and 'contention-free'.

≪Contention-based RA (CBRA) procedure≫
FIG. 1 is a diagram for explaining a CBRA procedure according to related art.

- RA preamble (or Msg1) transmission The UE, in action 101, transmits the RA preamble.
The UE selects one of the available 64-Ncf contention-based RA preambles.
Ncf is the number of RA preambles reserved for contention-free access.
Contention-based RA preambles are optionally divided into two groups.
With two groups configured, the UE selects a group based on the size of message 3 that the UE can send.
The initial RA preamble transmit power is set based on open-loop estimation after compensating for path loss.

・RA response (RA response, hereinafter, RAR) or Msg2
In operation 102, the evolved node B (NB) communicates via a physical downlink shared channel (PDSCH) addressed with a random access-radio network temporary identifier (RA-RNTI). RAR Send.
RA-RNTI identifies the time-frequency slot in which the RA preamble was detected by the eNB.
The RAR carries an RA preamble identifier, timing alignment information, a temporary C-RNTI (cell-radio network temporary identifier) and a UL grant for message 3.
The RAR may also include a backoff indicator that instructs the UE to back off for a period of time before reattempting the RA attempt.
RARs are sent in RAR windows.

FIG. 3 is a diagram for explaining RA preamble transmission and RAR window according to related art.
As shown in FIG. 3, the RAR window starts at subframe 'x+3' for the RA preamble transmitted in subframe 'x'.
The RAR window size is configurable.

- Scheduled uplink (UL) transmission on UL shared channel (SCH) (or Msg3) At operation 103, the UE performs a scheduled transmission.
Scheduled UL transmissions are used to send messages such as RRC Connection Request, RR Connection Reconfiguration Request, RRC Handover Confirmation, Scheduling Request, and so on.
It also contains the UE identity (ie C-RNTI or S-TMSI (system architecture evolution-temporary mobile subscriber identity) or random number).
HARQ (hybrid automatic repeat request) is used for such transmission.
The message sent in the scheduled UL transmission is typically Msg3.

・Contention Resolution Message (or Msg4)
The eNB at operation 104 sends a conflict resolution message.
The conflict resolution message is more generally Msg4.
Contention resolution messages use HARQ and are addressed to the C-RNTI (if included in Msg3) or the Temporary C-RNTI (if C-RNTI is not included in Msg3).
Upon successful decoding of contention resolution messages, HARQ feedback is only sent by UEs that track their UE ID (or C-RNTI).

Contention-free RA (CFRA) procedure FIG. 2 is a diagram for explaining the CFRA procedure according to the related art.
The CFRA procedure is used in scenarios such as handovers where low latency is required, timing advance establishment for secondary cells (Scells), and so on.

Referring to FIG. 2, the eNB allocates a contention-free RA preamble to the UE in operation 201 with dedicated signaling.
The UE transmits the assigned contention-free RA preamble in operation 202 .
The eNB in operation 203 transmits the RAR via PDSCH addressed in the RA-RNTI.
RAR carries RA preamble identifier and timing alignment information.
A RAR may also include a UL authorization.
RAR is sent in the RAR window, similar to the CBRA procedure.
The CFRA procedure is terminated after receiving the RAR.

It should be noted that during the contention-free (ie, contention-free preamble assigned) random access procedure, the UE transmits and retransmits the contention-free RA preamble until the random access procedure is completed.

≪Problem Description≫
At higher frequencies, beamforming is needed to compensate for high path loss.
The UE/gNB needs to transmit and receive a physical random access channel (PRACH) preamble and Msg3 using beamforming.
GNB/UE needs to transmit and receive RAR & Msg4 with beampomming.
UEs and gNBs can support multiple transmit (TX)/receive (RX) beams, with each TX/RX beam covering a specific coverage area.
In case of beamformed PRACH preamble transmission, the DL TX beam (ie gNB TX beam) is indicated by the UE during the PRACH preamble transmission.
Based on the received PRACH preamble transmission, the gNB identifies a DL TX beam for transmitting Msg2.

The UE identifies the DL TX beam based on how many times the DL synchronization signal, reference signal or broadcast channel is transmitted in case of beamforming system.
One or multiple DL TX beams are used to transmit DL synchronization signals, reference signals, or broadcast channels for each time-occasion.
Time occasions for transmitting synchronization signals (i.e., primary synchronization signal (PSS)/synchronization signal (SSS) and primary broadcast channel (PBCH)) using one or multiple DL TX beams is a sync signal (SS) block.

The network periodically transmits DL synchronization signals and PBCH with a number of SS blocks.
The GNB may include one or multiple occasions for SS blocks and a subset of random access channel (RACH) resources (i.e., time/frequency resources are further referred to as PRACH or RA occasions) and/or PRACH preambles ( RA preambles or random access preambles) to establish associations between subsets of the index.
Such association is configured in RACH configuration signaled in system information dedicated RRC signaling (eg handover command).
The UE selects the PRACH preamble and/or PRACH resource (or PRACH occasion) corresponding to the SS block for which the UE received the DL synchronization signal.
Similar to the SGS block, the gNB has one or many CSI-RS (Channel State Information-Reference Signal) (CSI-RS is transmitted using TX beamforming) and PRACH resources (i.e., time/ The frequency resources further establish associations between subsets of PRACH occasions or RA occasions) and/or subsets of PRACH preamble indices.
Such association is configured in RACH configuration signaled in system information or dedicated RRC signaling (eg handover command).
The UE selects PRACH preambles and/or PRACH resources (or PRACH occasions) corresponding to the received CSI-RS signals.

The first issue is how the UE selects SS blocks for PRACH preamble and/or PRACH resource (or PRACH occasion) selection during initial PRACH preamble transmission.
A second problem is that the UE is unable to successfully receive a PRACH retransmission, i.e., the PRACH preamble and/or PRACH resources (or PRACH occasions) after the UE has transmitted the PRACH preamble and has not been able to successfully receive the RAR. A method of selecting SS blocks for selection.
A third problem is how to select SS blocks for PRACH preamble and/or PRACH resource (or PRACH occasion) selection during handover to the target cell for PRACH (re)transmission by the UE in the target cell. where the handover command is appended to the contention-based PRACH preambles and/or PRACH resources (or PRACH occasions) for all SS blocks and the contention-free PRACH preambles and/or PRACH resources (or PRACH occasions).

The above information is presented as background information only to aid in understanding the present invention. No determination is made and no claims are made as to whether any of the above is applicable in the prior art in connection with the present invention.

One aspect of the present invention is to overcome at least the problems and/or disadvantages mentioned above and to provide at least the advantages described below.
Accordingly, one aspect of the present invention is to provide a communication method and system for converging fifth generation (5G) communication systems that support higher data rates than fourth generation (4G) systems.

According to a first aspect of the present invention, there is provided a method performed by a terminal in a wireless communication system, in which contention-based random access (RA) configuration information and a synchronization signal (SS) block (hereinafter referred to as an SS block) are transmitted from a base station ), and receiving from the base station contention-free RA configuration information and information of at least one RA preamble associated with each of the SS blocks. and the configuration information of the contention-free RA includes information of contention-free RA resources associated with the SS block, and signal quality greater than the threshold within the SS blocks associated with the contention-free RA resources. is available, selecting a first SS block from among the at least one SS block associated with the contention-free RA resource; and the at least one selecting a first RA preamble corresponding to the selected first SS block based on the information of one RA preamble; and a signal greater than the threshold within the SS block associated with the contention-free RA resource. selecting at least one SS block with signal quality greater than the threshold from among SS blocks associated with contention-based RA resources if the at least one block with quality is not available; selecting a second SS block from among the at least one SS block associated with underlying RA resources; and randomly with equal probability from among at least one competing RA preamble associated with the selected second SS block. selecting a 2RA preamble; selecting a physical random access channel (PRACH) occurrence based on the selected first SS block or the selected second SS block; and C. transmitting the first RA preamble or the second RA preamble on a selected PRACH occasion .

According to a second aspect of the present invention, a method performed by a base station of a wireless communication system, comprising: sending to the terminal information of a threshold for the SS block, sending to the terminal contention-free RA configuration information and information of at least one RA preamble associated with each of the SS blocks; , receiving a first RA preamble or a second RA preamble from the terminal on a physical random access channel (PRACH) occurrence selected based on the first SS block or the second SS block; at least one of the configuration information of contention RA includes information of contention-free RA resources associated with the SS block, and having signal quality greater than the threshold within the SS blocks associated with the contention-free RA resources; If SS blocks are available, the first SS block is selected from among the at least one SS block associated with the contention-free RA resource, and a first RA preamble corresponding to the selected first SS block is the respective said at least one SS selected based on said information of said at least one RA preamble associated with said SS block of said SS having signal quality greater than said threshold within said SS block associated with said contention-free RA resource. If blocks are not available, at least one SS block having a signal quality greater than the threshold is identified within an SS block associated with a contention-based RA resource, and the second SS block is associated with the contention-based RA resource. and the second RA preamble is randomly selected from among at least one competing RA preamble associated with the selected second SS block with the same probability. and

According to a third aspect of the present invention, there is provided a terminal of a wireless communication system, comprising: a transceiver; Receive threshold information for block (hereinafter referred to as SS block) selection, contention-free RA configuration information from the base station, and at least one RA preamble information associated with each of the SS blocks. wherein the configuration information of the contention-free RA includes information of contention-free RA resources associated with SS blocks, and signal quality greater than the threshold within the SS blocks associated with the contention-free RA resources. selecting a first SS block from among the at least one SS block associated with the contention-free RA resource, if at least one SS block having at least one SS block is available, and the at least one RA preamble associated with each of the SS blocks; selecting a first RA preamble corresponding to the selected first SS block, having a signal quality greater than the threshold within the SS block associated with the contention-free RA resource, based on the information of the at least identifying at least one SS block having a signal quality greater than the threshold in SS blocks associated with contention-based RA resources if one SS block is not available; selecting a second SS block from among one SS block; selecting a second RA preamble randomly with equal probability from among at least one competing RA preamble associated with said selected second SS block; selecting a physical random access channel (PRACH) occurrence based on the first SS block or the selected second SS block, and sending the base station the first RA preamble or the second RA preamble on the selected PRACH occasion; and a controller for transmitting the

According to a fourth aspect of the present invention, a base station of a wireless communication system, comprising: a transceiver; , SS block) threshold information for selection of the SS block) to the terminal; and receive a first RA preamble or a second RA preamble from the terminal on a physical random access channel (PRACH) occurrence selected based on the first SS block or the second SS block. wherein the configuration information of the contention-free RA includes information of contention-free RA resources associated with the SS blocks, and signal quality greater than the threshold within the SS blocks associated with the contention-free RA resources. a first SS block is selected from among the at least one SS block associated with the contention-free RA resource, if at least one SS block having at least one SS block is available, and a first RA preamble corresponding to the selected first SS block; is selected based on the information of the at least one RA preamble associated with each of the SS blocks and has a signal quality greater than the threshold within the SS blocks associated with the contention-free RA resources. If at least one SS block is not available, at least one SS block having a signal quality greater than the threshold is identified among the SS blocks associated with contention-based RA resources, and the second SS block is identified as the contention-based RA resource. selected from among the at least one SS block associated with underlying RA resources, and the second RA preamble is randomly selected with equal probability from among at least one competing RA preamble associated with the selected second SS block; characterized by being

It is a figure for demonstrating the procedure of CBRA by related technology. It is a figure for demonstrating the procedure of CFRA by related technology. FIG. 2 illustrates RA preamble transmission and RAR window according to related art; 4 is a flow chart for explaining high level UE operation according to an embodiment of the present invention; 4 is a flow chart illustrating UE operation for RACH transmission and retransmission based on method 1 according to embodiments of the present invention; 4 is a flow chart illustrating UE operation for RACH transmission and retransmission based on Method 2 according to embodiments of the present invention; 4 is a flow chart illustrating UE operation for RACH transmission and retransmission based on Method 3 according to embodiments of the present invention; 4 is a flow chart illustrating UE operation for RACH transmission and retransmission based on Method 4 according to embodiments of the present invention; Figure 4 is a flow chart illustrating UE behavior for RACH transmission and retransmission based on method 5 according to embodiments of the present invention; Figure 4 is a flow chart illustrating UE operation for RACH transmission and retransmission based on method 6 according to embodiments of the present invention; Figure 4 is a flow chart illustrating UE operation for RACH transmission and retransmission based on method 7 according to embodiments of the present invention; Figure 4 is a flow chart illustrating UE operation for RACH transmission and retransmission based on method 8 according to embodiments of the present invention; Figure 4 is a flow chart illustrating UE operation for RACH transmission and retransmission based on method 9 according to embodiments of the present invention; Figure 4 is a flow chart illustrating UE operation for RACH transmission and retransmission based on method 10 according to embodiments of the present invention; Figure 4 is a flow chart illustrating UE operation for RACH transmission and retransmission based on method 11 according to embodiments of the present invention; Figure 4 is a flow chart illustrating UE operation for RACH transmission and retransmission based on method 12 according to embodiments of the present invention; Figure 4 is a flow chart illustrating UE operation for RACH transmission and retransmission based on method 13 according to embodiments of the present invention; Figure 4 is a flow chart illustrating UE operation for RACH transmission and retransmission based on method 14 according to embodiments of the present invention; Figure 4 is a flow chart illustrating UE operation for RACH transmission and retransmission based on method 15 according to embodiments of the present invention; Figure 4 is a flow chart illustrating UE operation for RACH transmission and retransmission based on method 16 according to embodiments of the present invention; Figure 4 is a flow chart illustrating UE operation for RACH transmission and retransmission based on method 17 according to embodiments of the present invention; Figure 4 is a flow chart illustrating UE operation for RACH transmission and retransmission based on method 18 according to embodiments of the present invention; Figure 4 is a flow chart illustrating UE operation for RACH transmission and retransmission based on method 19 according to embodiments of the present invention; Figure 2 is a flow chart illustrating UE operation for RACH transmission and retransmission based on method 20 according to embodiments of the present invention; Figure 2 is a flow chart illustrating UE operation for RACH transmission and retransmission based on method 20 according to embodiments of the present invention; FIG. 4 is a diagram for explaining an example in which a UE transmits Msg1 only once before a RAR window; FIG. 4 is a diagram for explaining an example in which multiple Msg1 transmissions are performed before the RAR window according to various embodiments of the present invention; FIG. 5 is a diagram illustrating another example in which multiple Msg1 transmissions are performed before the RAR window according to various embodiments of the present invention; FIG. 4 is a diagram to illustrate multiple Msg1 transmissions before or while waiting for RAR for the first transmitted Msg1 under Option 1 according to an embodiment of the present invention; FIG. 4 is a diagram for explaining multiple Msg1 transmissions before or while waiting for RAR for the first transmitted Msg1 under option 2 according to an embodiment of the present invention; FIG. 4 is a diagram for explaining multiple Msg1 transmissions before or while waiting for RAR for the first transmitted Msg1 under option 2 according to an embodiment of the present invention; FIG. 4 is a diagram to illustrate multiple Msg1 transmissions before or while waiting for RAR for the first transmitted Msg1 under Option 3 according to an embodiment of the present invention; 1 is a block diagram showing a schematic configuration of a UE according to an embodiment of the present invention; FIG. It is a block diagram showing a schematic configuration of a BS according to an embodiment of the present invention.

The following description with reference to the accompanying drawings is provided to aid in a comprehensive understanding of the various embodiments of the invention as defined by the claims and equivalents thereof.
Although it contains various specific details to aid understanding, this should be viewed as exemplary only.
Accordingly, those skilled in the art will appreciate that various changes and modifications to the various embodiments described herein can be made without departing from the scope and spirit of the invention.
Moreover, descriptions of well-known functions and constructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are not limited to bibliographical meanings and are used to provide a clear and consistent understanding of the invention by the inventors.
Accordingly, it will be appreciated by those skilled in the art that the following description of various embodiments of the invention is provided for purposes of illustration only, and not to limit the invention as defined by the appended claims and equivalents thereof. it should be obvious.

It should be understood that the singular forms "a,""an," and "the" include plural referents unless the context clearly dictates otherwise.
Thus, for example, reference to "a component surface" includes reference to one or more of such surfaces.
The term "substantially" does not require that the recited property, parameter or value be exactly achieved, but includes deviations including, for example, tolerances, measurement errors, measurement accuracy limits and other factors known to those of skill in the art. or that variation can occur in an amount that does not eliminate the effect the property is intended to provide.

Those of ordinary skill in the art will understand that blocks of flowcharts (or sequence diagrams) and combinations of flowcharts can be represented and executed by computer program instructions.
Such computer program instructions can be loaded onto the processor of a general purpose computer, special purpose computer or programmable data processing apparatus.
When the loaded program instructions are executed by the processor, it creates means for performing the functions illustrated in the flowcharts.
The computer program instructions may be stored in a computer readable memory usable by a specialized computer or programmable data processing device to create an article of manufacture that performs the functions illustrated in the flowcharts.
The computer program instructions can be loaded onto a computer or programmable data processing device so that when executed as a process, it can perform the functions illustrated in the flowcharts.

Blocks in the flowcharts may correspond to modules, segments or code containing one or more executable instructions that implement one or more logical functions, or may correspond to portions thereof.
In some cases, the functions described by the blocks may be performed in steps other than those listed.
For example, two blocks listed in a sequence can be executed simultaneously or in reverse order.

In this description, the words "unit", "module", etc. refer to a software component or hardware such as, for example, a field-programmable gate array (FPGA) or an application-specific integrated circuit (ASIC) capable of performing a function or operation. Refers to hardware components.
However, "units" and the like are not limited to hardware or software.
A unit or the like may reside in an addressable storage medium or may be configured to drive one or more processors.
Such units may be software components, object-oriented software components, class components, task components, processes, functions, attributes, procedures, subroutines, program code segments, drivers, firmware, microcode, circuits, data, databases, Refers to a data structure, table, array or variable.
The functionality provided by the components and units may be a combination of smaller components and units and may be combined with other components and units to form larger components and units.
Components and units can be configured to drive devices or one or more processors in a secure multimedia card.

Prior to the detailed description, terms or definitions necessary to understand the invention are explained.
However, such terms should be interpreted in a non-restrictive manner.
A “base station (BS)” is an entity that communicates with a user equipment (UE), and includes a BS, a base transceiver station (BTS), a Node B (NB), It may be referred to as an eNB (evolved NB), an access point (AP), a 5G NB (5G NB) or a gNB.
A “UE” is an entity that communicates with a BS and may be referred to as a UE, device, mobile station (MS), mobile equipment (ME), or terminal.

FIG. 4 is a flow chart illustrating high level UE operation according to an embodiment of the present invention.
The operation of the UE illustrated in FIG. 4 will be discussed in detail in various ways that are discussed further below.

Referring to FIG. 4, the UE first determines at operation 410 whether access latency is an issue for random access channel (RACH) procedures.
For example, for low latency applications, UEs certainly have to complete their RACH procedures quickly, so access latency is certainly an issue.
However, in some applications where the UE is only concerned about sending reports to the BS, but not at the same time, such as metering applications, the UE waits for access. You can conclude that time is not an issue for your network entry.

When access latency is really important, the UE has to enter the network as soon as possible, so the UE decides to RACH on the appropriate SS block in operation 420 (appropriate The exact definitions and methods selected are discussed in detail below).
Otherwise, the UE shall be sent out of all possible SS blocks transmitted by the gNB, i.e. (indicated via the parameter L predefined for the frequency band given in the 3GPP specifications or system information or determined in operation 430 after finding the SS block after scanning and measuring all SS blocks transmitted by the base station (indicated via the parameter 'SSBPositionsInBurst' signaled by the gNB in the RRC message).

In addition, such a determination also determines whether the UE has to scan all UE receive (Rx) beams in further action (421 or 431) or can select one RX beam at once. It can be extended to beamforming and is satisfied when the UE finds a suitable SS block corresponding to such selected UE Rx beam in operation (422 or 432).
The RACH procedure performance may indeed depend on such selection of SS blocks, but in most cases the UE only camps on the network as soon as possible when access latency is an issue. will only worry about

Such a procedure for finding a suitable SS block can be left in the full UE implementation, supported by the gNB, or fixed to the specification via an explicit threshold.
Various ways in which the reference signals received power (RSRP) threshold may be indicated to the UE are discussed below.
If RSRQ (reference signal received quality) measurements or SINR (signal-to-interference-plus-noise ratio) measurements are used for the RACH procedure, the thresholds need to be indicated and signaled appropriately. be.
For simplicity, the rest of the disclosure will only refer to thresholds.

For the initial access RACH procedure, the gNB may indicate the threshold for selecting SS blocks to the UE by one or a combination of the following mechanisms.

1) Fixed in specification.
2) RMSI (remaining minimum system information) (eg, SIB 1) indication.
3) RACH set indication.

The gNB has complete control over this network loading, cell edge radius, placement conditions, etc.
Therefore, the gNB decides to change the threshold used for proper SS block selection for various UEs by explicit indication via RMSI or RACH configuration information.
The values fixed in the specification may or may not work in all situations.
Furthermore, for fairness, the gNB determines such thresholds uniformly across all users, so explicit indication may be desirable.
Such thresholds are expressed explicitly as absolute or differential values relative to some reference value such as -100 dBm (as an example) which may be fixed in the specification.
Such difference reporting helps reduce the number of bits in the manner in which such thresholds are indicated.

In the case of sub-6GHz systems where multiple SS blocks are provided mainly for coherent combining and better PBCH demodulation, it does not matter what RACH resource the UE chooses. do not have.
This is explicitly indicated to the user by the gNB.
Such issues of SS block selection are especially important for mmWave systems where the UE must select a gNB specific beam/direction/SS-block for RACH.

4) for retransmission,
In addition, the threshold is also indicated in the RAR if anything changes on the gNB side.
The same thresholds indicated in the initial access procedure continue to be used for the full RACH procedure and for any retransmissions required in the same case.
Besides, an explicit indication in the RAR message indicates to the UE that it is used for additional retransmission of the RACH preamble.
This allows flexibility from the gNB side to dynamically change the threshold based on channel conditions/network loading etc.

5) For contention-free (hereinafter referred to as CF),
Indicate threshold in handover command for CSI-RS RACH 6) for CF,
Such thresholds are fixed in the specification.
7) for CF,
Full UE realization without target gNB assistance.
8) for CF,
Dedicated UE specific signaling indicates the threshold.

In the case of CF RACH based on CSI-RS, different thresholds indicate to the UE that they are suitable for CSI-RS resources/beams.
This is because the CSI-RS beams are opposite to the SS block-based beams and can have different settings, ie, "wider" versus "narrower" settings.
In such cases, a suitable threshold for this must also be indicated.
Except for (6) and (7) above which are the same as for the SS block, in the CF case the target cell must indicate the threshold used.
Such a threshold is therefore indicated in the handover command.
In the case of such a handover, the target cell gives the UE two thresholds, i.e.,
a) CSI-RS based thresholds and b) SS based thresholds can be indicated.
In other words, the SS threshold differs from the CSI-RS threshold due to beamforming design differences.

9) if CF,
A fall back RACH based on the SS-based threshold is indicated in the handover command.
10) if CF,
A fallback RACH based on SS-based thresholds is indicated via the target cell's SI.
11) if CF,
Fallback RACH based on SS-based threshold is fixed in the specification.
12) if CF,
A fallback RACH based on SS-based threshold is indicated via the target cell's RACH setting.

Options 8-11 show various means of indicating such SS-based thresholds in the case of CF RACH performed in the case of handover procedures.
Such thresholds are also indicated via the SI when the UE interprets the system information (SI) of the target cell.
Also, such a threshold can be included in the target cell's RACH configuration when the RACH configuration is provided to the UE.

13) The SS threshold for initial access is different from the SS threshold for handover/CF cases.
Note that the thresholds for initial access and handover cases are different to support fast access to the network, or faster handovers and lower interruption times, etc. FIG.
For example, a conservative threshold may be provided in case of handover to allow 0ms handover interruption time.

14) In the absence of indication, the UE assumes the same threshold for initial access and handover to SS-based mechanisms.
If no explicit indication is given to the UE, the UE uses the available threshold given in previous phases such as initial access.

15) For beam recovery RACH, which can be based on CSI-RS or SS-blocks,
The thresholds that need to be the same are indicated to the UE via the RRC connection setup procedure (ie in the RRC reconfiguration message).
Such a threshold for beam recovery differs from other thresholds because the UE must recover quickly from beam failure via the L1 mechanism.
When beam recovery is initiated by the network, the threshold is communicated to the UE via UE-specific signaling, i.e. Downlink Control Information (DCI) or Medium Access Control (MAC), appropriate for the specific time the procedure is triggered. shown.

After setting the context for selecting the best or suitable SS block, the UE behavior for RACH transmissions and retransmissions using the available measurements is detailed below.

≪Method 1≫
FIG. 5 is a flow chart illustrating UE operation for RACH transmission and retransmission based on method 1 according to an embodiment of the present invention.

Referring to FIG. 5, at operation 501, the UE selects the SS block with the highest signal quality for initial PRACH preamble transmission.
During the random access procedure, the first PRACH preamble transmission shall be the initial PRACH preamble transmission.
Signal quality is measured over the resources of the PSS and/or SSS for the PBCH and/or the SS block carrying the demodulation reference signal (DMRS).
The signal quality may be RSRP, RSRQ, or a received signal strength indicator (RSSI).
In one embodiment, the UE selects the SS block with the highest signal quality among all SS blocks transmitted by the gNB.
In another embodiment, the UE selects the SS block with the highest signal quality among all SS blocks for which measurements are available.

Next, at operation 502, the UE transmits a PRACH preamble (ie, Msg1) by selecting the PRACH preamble and/or PRACH resource (or PRACH occasion) corresponding to the selected SS block.
The PRACH preamble is referred to as RA preamble or RACH preamble.

Once an SS block is associated with a PRACH preamble, the UE randomly selects a PRACH preamble from the PRACH preambles corresponding to the selected SS block.
The UE selects the earliest available PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions).
In one embodiment, the UE randomly selects one PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions).
If multiple frequency division multiplexed PRACH resources (or PRACH occasions) are available simultaneously, the UE selects one with equal probability from the multiple frequency division multiplexed PRACH resources (or PRACH occasions) available in the selected time slot. Randomly select a PRACH resource (or PRACH occasion).

Once an SS block is associated with a PRACH resource (or PRACH occasion), the UE selects the earliest available PRACH resource (or PRACH occasion) from the PRACH resource (or PRACH occasion) corresponding to the selected SS block.
In one embodiment, the UE randomly selects one PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions) corresponding to the selected SS block.
If multiple frequency division multiplexed PRACH resources (or PRACH occasions) are available simultaneously corresponding to the selected SS block, the UE can select from the available multiple frequency division multiplexed PRACH resources (or PRACH occasions) with equal probability. randomly select one PRACH resource (or PRACH occasion).
The UE randomly selects a PRACH preamble from the configured set of PRACH preambles with equal probability.

Once an SS block is associated with a PRACH preamble and PRACH resources, the UE randomly selects a PRACH preamble from the PRACH preambles corresponding to the selected SS block.
In one embodiment, the UE randomly selects one PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions) corresponding to the selected SS block.
The UE selects the earliest available PRACH resource (or PRACH occasion) corresponding to the selected SS block.
If multiple frequency division multiplexed PRACH resources (PRACH occasions) corresponding to the selected SS block are available at the same time, the UE may select one from the multiple frequency division multiplexed PRACH resources (or PRACH occasions) available with equal probability. Randomly select one PRACH resource (PRACH occasion).

To calculate the power to transmit the PRACH, the UE estimates the pathloss based on the signal received on the selected SS block.
After transmitting Msg1, in operation 503 the UE determines whether the RAR corresponding to the Msg1 transmission (ie Msg2) was successfully received.
If the UE successfully receives the RAR, there is no need to resend Msg1 in operation 504 .
If the UE is unable to receive the RAR, in operation 505 the UE determines whether it has performed the maximum number of allowed Msg1 transmissions.
If the UE has not yet performed the maximum number of allowed Msg1 transmissions, the UE retransmits Msg1.
If the UE has performed the maximum number of allowed Msg1 transmissions, the UE will not retransmit Msg1.
Between retransmissions, the UE does not reselect SS blocks.
The UE uses the same SS block that was selected for the initial transmission.
The SS block is selected when the random access procedure is initiated, and the same SS block is used for PRACH preamble and/or PRACH resource (or PRACH occasion) selection for every (re)transmission of Msg1 during the random access procedure. and for path loss estimation.

In alternative embodiments of such methods, CSI-RS can be used instead of SS blocks.
The UE selects the CSI-RS instead of the SS block using the same procedure as described above for the SS block.
The UE selects PRACH preambles and/or PRACH resources (PRACH occasions) from the PRACH preambles and/or PRACH resources (PRACH occasions) corresponding to the selected CSI-RS.

≪Key point≫
The UE selects the SS block (or CSI-RS) with the highest signal quality when the random access procedure is initiated.
The UE selects the SS block (or CSI-RS) selected for PRACH preamble and/or PRACH resource (PRACH occasion) selection and path loss estimation for every (re)transmission of Msg1 during the random access procedure. Use

≪Method 2≫
FIG. 6 is a flow chart illustrating UE operation for RACH transmission and retransmission based on Method 2 according to an embodiment of the present invention.

Referring to FIG. 6, at operation 601, the UE selects a suitable SS block for initial PRACH preamble transmission.
An SS block is suitable if the signal quality of the SS block is greater than a threshold 'SSBlockThreshold'.
In an embodiment, an SS block is suitable if the signal quality of the SS block is greater than or equal to a threshold 'SSBlockThreshold'.
The SSBlockThreshold is set by the network in system information (e.g. with PRACH settings or in RMSI) or handover commands or dedicated RRC signaling.
Signal quality is measured over resources of SS blocks carrying PSS and/or SSS and/or DMRS for PBCH.
Signal quality may be RSRP or RSRQ or RSSI.
If multiple SS blocks are suitable, the UE can select the SS block in one of the following manners.

The UE selects the SS block with the highest signal quality among the suitable SS blocks.
The UE selects the SS block corresponding to the earliest available PRACH resource (or PRACH occasion) in time among the suitable SS blocks.
The UE randomly selects one of the SS blocks with equal probability among the appropriate SS blocks.
The UE selects any SS block among the appropriate SS blocks.
The UE selects one of the following methods based on indications from the network (signaled as part of PRACH configuration in SI and/or handover command and/or dedicated RRC signaling).
That is, select the SS block with the highest signal quality among the suitable SS blocks, or select the SS block corresponding to the earliest available RACH resource (or PRACH occasion) among the suitable SS blocks, or Randomly select any one of the SS blocks with the same probability among the SS blocks.

Next, at operation 602, the UE transmits a PRACH preamble (ie, Msg1) by selecting a PRACH preamble and/or PRACH resource (or PRACH occasion) corresponding to the selected SS block.
Once an SS block is associated with a PRACH preamble, the UE randomly selects a PRACH preamble from the PRACH preambles corresponding to the selected SS block.
The UE selects the earliest available PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions).
In one embodiment, the UE randomly selects one PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions).
If multiple frequency division multiplexed PRACH resources (or PRACH occasions) are available in time, the UE selects one PRACH resource (or PRACH occasion) is randomly selected.

Once an SS block is associated with a PRACH resource (or PRACH occasion), the UE selects the earliest available PRACH resource (or PRACH occasion) from the PRACH resource (or PRACH occasion) corresponding to the selected SS block.
In one embodiment, the UE randomly selects one PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions) corresponding to the selected SS block.
If multiple frequency division multiplexed PRACH resources (or PRACH occasions) corresponding to the selected SS block are available, the UE may select one from the multiple frequency division multiplexed PRACH resources (or PRACH occasions) available with equal probability. randomly select one PRACH resource (or PRACH occasion).
The UE randomly selects a PRACH preamble from the configured set of PRACH preambles with equal probability.

Once an SS block is associated with a PRACH preamble and PRACH resources, the UE randomly selects a PRACH preamble from the PRACH preambles corresponding to the selected SS block.
The UE selects the earliest available PRACH resource (or PRACH occasion) from the PRACH resources (or PRACH occasions) corresponding to the selected SS block.
In one embodiment, the UE randomly selects one RPACH resource (PRACH occasion) from the configured PRACH resources (or PRACH occasions) corresponding to the selected SS block.
If multiple frequency division multiplexed PRACH resources (or PRACH occasions) corresponding to the selected SS block are available, the UE may select one from the multiple frequency division multiplexed PRACH resources (or PRACH occasions) available with equal probability. Randomly select one PRACH resource (PRACH occasion).

To calculate the power for transmitting the PRACH, the UE estimates the pathloss based on the signal received on the selected SS block.
After transmitting Msg1, in operation 603 the UE determines whether the RAR corresponding to the Msg1 transmission (ie Msg2) was successfully received.
If the UE successfully receives the RAR, there is no need to retransmit Msg1 at operation 604 .
If the UE is unable to receive the RAR, in operation 605 the UE determines whether it has performed the maximum number of Msg1 transmissions allowed by the UE.
If the UE has not yet performed the maximum number of allowed Msg1 transmissions, the UE retransmits Msg1.
If the UE has performed the maximum number of allowed Msg1 transmissions, the UE will not retransmit Msg1.
Between retransmissions, the UE does not reselect SS blocks.
The UE uses the same SS block that was selected for the initial transmission.
An appropriate SS block is selected when the random access procedure is initiated, and during the random access procedure PRACH preamble and/or PRACH resource (PRACH occasion) selection and path loss estimation for every (re)transmission of Msg1. The same SS block is used for
If no suitable SS block is found, the UE reselects a suitable SS block during retransmissions as described below.

With the procedure described above, the UE may not be able to find any suitable SS block.
In this case, the UE either:
UE does not send Msg1.
Additionally, the UE triggers cell reselection for idle/inactive state and RLF (ie connection reconfiguration) for connected state.
The UE selects the SS block for which measurements are available or the SS block with the highest signal quality among all SS blocks.
In this case (i.e., when no suitable SS block is selected), during the retransmission of Msg1, the UE will receive an SS block if the SS block for the previous transmission is still not suitable and another suitable SS block is found. change blocks.
In one embodiment, the UE is allowed to send Msg1 without selecting a suitable SS block between the 'N' number.
Parameter N is either predefined or signaled by the network.

The UE delays Msg1 transmission until the UE finds a suitable SS block.
In one embodiment, the UE may delay the Msg1 transmission for a maximum time period 'T'.
The time period T is configured by the network in system information (e.g. with PRACH configuration or in RMSI) or handover commands or dedicated RRC signaling.
After this time expires, the UE triggers cell reselection for idle/inactive state and RLF for connected state (ie, connection reconfiguration) if a suitable SS block is still not found.
Alternatively, if a suitable SS block is still not found, after this time has expired the UE has the highest signal quality among all SS blocks or among SS blocks for which measurements are available. Select SS block.

In alternative embodiments of this method, CSI-RS can be used instead of SS blocks.
The UE selects the CSI-RS instead of the SS block using the same procedure as described above for the SS block.
The UE selects PRACH preambles and/or PRACH resources (PRACH occasions) from the PRACH preambles and/or PRACH resources (or PRACH occasions) corresponding to the selected CSI-RS.

≪Key point≫
1) The UE selects a suitable (signal quality>SSBlockThreshold) SS block (or CSI-RS) when the random access procedure is initiated.
The UE uses the selected SS block (or CSI-RS) for PRACH preamble and/or PRACH resource (PRACH occasion) selection and path loss estimation for every (re)transmission of Msg1 during the random access procedure. .
2) If no suitable SS block is found, the UE selects the SS block (or CSI-RS) with the highest signal quality.
3) no suitable SS block (or CSI-RS) was used for the previous transmission, the SS block (or CSI-RS) for the previous transmission is still not suitable, and another suitable SS block ( or CSI-RS) is found, the UE changes the SS block (or CSI-RS).
4) If no suitable SS block (or CSI-RS) is found, the UE reselects the cell.
5) The UE delays Msg1 transmission until a suitable SS block (or CSI-RS) is found.
6) If no suitable SS block (or CSI-RS) is found, the UE delays Msg1 transmission for a defined time period.
If no suitable SS block (or CSI-RS) is found after that time period, the UE triggers cell reselection for idle/inactive state and RLF for connected state (ie connection reconfiguration).

≪Method 3≫
FIG. 7 is a flow chart illustrating UE operation for RACH transmission and retransmission based on Method 3 according to an embodiment of the present invention.

Referring to FIG. 7, at operation 701, the UE selects the SS block with the highest signal quality for initial PRACH preamble transmission.
Signal quality is measured via resources of SS blocks carrying PSS and/or SSS and/or DMRS for PBCH.
Signal quality may be RSRP or RSRQ or RSSI.
In one embodiment, the UE selects the SS block with the highest signal quality among all SS blocks transmitted by the gNB.
In another embodiment, the UE selects the SS block with the highest signal quality among all SS blocks for which measurements are available.

Next, at operation 702, the UE transmits a PRACH preamble (ie, Msg1) by selecting the PRACH preamble and/or PRACH resource (or PRACH occasion) corresponding to the selected SS block.

Once an SS block is associated with a PRACH preamble, the UE randomly selects a PRACH preamble from the PRACH preambles corresponding to the selected SS block.
The UE selects the earliest available PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions).
In one embodiment, the UE randomly selects one PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions).
If multiple frequency division multiplexed PRACH resources (or PRACH occasions) are available simultaneously, the UE may select one PRACH resource (or PRACH occasion) with equal probability from the multiple frequency division multiplexed PRACH resources (or PRACH occasions) available. ) is randomly selected.

Once an SS block is associated with a PRACH resource (or PRACH occasion), the UE selects the earliest available PRACH resource (or PRACH occasion) from the PRACH resource (or PRACH occasion) corresponding to the selected SS block.
In one embodiment, the UE randomly selects one PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions) corresponding to the selected SS block.
If multiple frequency division multiplexed PRACH resources (or PRACH occasions) are available within the time corresponding to the selected SS block, the UE can select the same frequency division multiplexed PRACH resource (or PRACH occasion) from the available multiple frequency division multiplexed PRACH resources (or PRACH occasions). Randomly select one PRACH resource (or PRACH occasion) with a probability of .
The UE randomly selects a PRACH preamble from the configured set of PRACH preambles with equal probability.

Once an SS block is associated with a PRACH preamble and PRACH resources, the UE randomly selects a PRACH preamble from the PRACH preambles corresponding to the selected SS block.
The UE selects the earliest available PRACH resource (or PRACH occasion) from the PRACH resources (or PRACH occasions) corresponding to the selected SS block.
In one embodiment, the UE randomly selects one PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions) corresponding to the selected SS block.
If multiple frequency division multiplexed PRACH resources (or PRACH occasions) corresponding to the selected SS block are available, the UE may select one from the multiple frequency division multiplexed PRACH resources (or PRACH occasions) available with equal probability. Randomly select one PRACH resource (PRACH occasion).

To calculate the power to transmit the PRACH, the UE estimates the pathloss based on the signal received on the selected SS block.
After transmitting Msg1, in operation 703 the UE determines whether the RAR corresponding to the Msg1 transmission (ie Msg2) was successfully received.
If the UE successfully receives the RAR, there is no need to resend Msg1 in operation 704 .
If the UE is unable to receive the RAR, in operation 705 the UE determines whether the maximum number of Msg1 transmissions allowed by the UE has been performed.
If the UE has not yet performed the maximum number of allowed Msg1 transmissions, the UE retransmits Msg1.
If the UE has performed the maximum number of allowed Msg1 transmissions, the UE will not retransmit Msg1.

During the retransmission, the UE determines whether the signal quality of the SS block previously selected for Msg1 transmission is greater than or equal to the threshold “SSBlockThreshold” at operation 706 .
If the signal quality of the SS block previously selected for Msg1 transmission is greater than or equal to the threshold 'SSBlockThreshold', the UE will not reselect the SS block.
The threshold is set by the network in system information (e.g. with PRACH settings or in RMSI) or handover commands or dedicated RRC signaling.
The UE uses the same SS block that was selected for the previous transmission for PRACH preamble and/or PRACH resource selection and pathloss estimation for retransmission (ie, the next Msg1 transmission).
During retransmission, if the signal quality of the SS block previously selected for Msg1 transmission is less than the threshold 'SSBlockThreshold', the UE reselects the SS block at operation 707 .
The UE selects the SS block with the highest signal quality among all SS blocks transmitted by the gNB.
In another embodiment, the UE selects the SS block with the highest signal quality among all SS blocks for which measurements are available.

In alternative embodiments of such methods, CSI-RS can be used instead of SS blocks.
The UE selects the CSI-RS instead of the SS block using the same procedure as described above for the SS block.
The UE selects PRACH preambles and/or PRACH resources (or PRACH occasions) from the PRACH preambles and/or PRACH resources (or PRACH occasions) corresponding to the selected CSI-RS.

≪Key point≫
The UE selects the SS block (or CSI-RS) with the highest signal quality when the random access procedure is initiated.
If the SS block (or CSI-RS) of the previous transmission is below the threshold based on the most recent measurement the SS block (or CSI-RS) with the highest signal quality is selected during retransmission, the UE reselects the SS block (or CSI-RS) between retransmissions.
The UE uses the PRACH preamble for transmission of Msg1 during the random access procedure and/or the selected SS block (or CSI-RS) for PRACH resource (or PRACH occasion) selection and path loss estimation.

≪Method 4≫
Figure 8 is a flow chart illustrating UE operation for RACH transmission and retransmission based on Method 4 according to an embodiment of the present invention.

Referring to FIG. 8, at operation 801, the UE selects the SS block with the highest signal quality for initial PRACH preamble transmission.
Signal quality is measured via resources of SS blocks carrying PSS and/or SSS and/or DMRS for PBCH.
Signal quality may be RSRP or RSRQ or RSSI.
In one embodiment, the UE selects the SS block with the highest signal quality among all SS blocks transmitted by the gNB.
In another embodiment, the UE selects the SS block with the highest signal quality among all SS blocks for which measurements are available.

Next, at operation 802, the UE transmits a PRACH preamble (ie, Msg1) by selecting a PRACH preamble and/or PRACH resource (or PRACH occasion) corresponding to the selected SS block.

Once an SS block is associated with a PRACH preamble, the UE randomly selects a PRACH preamble from the PRACH preambles corresponding to the selected SS block.
The UE selects the earliest available PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions).
In one embodiment, the UE randomly selects one RPACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions).
If multiple frequency division multiplexed PRACH resources (or PRACH occasions) are available, the UE selects one PRACH resource (or PRACH occasion) with equal probability from the multiple frequency division multiplexed PRACH resources (or PRACH occasions) available. randomly select.

Once an SS block is associated with a PRACH resource (or PRACH occasion), the UE selects the earliest possible PRACH resource (or PRACH occasion) from the PRACH resource (or PRACH occasion) corresponding to the selected SS block.
In one embodiment, the UE randomly selects one RPACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions) corresponding to the selected SS block.
If multiple frequency division multiplexed PRACH resources (or PRACH occasions) are available within the time corresponding to the selected SS block, the UE can select the same frequency division multiplexed PRACH resource (or PRACH occasion) from the available multiple frequency division multiplexed PRACH resources (or PRACH occasions). Randomly select one PRACH resource (or PRACH occasion) with a probability of . The UE randomly selects a PRACH preamble from the configured set of PRACH preambles with equal probability.

Once an SS block is associated with a PRACH preamble (or PRACH occasion) and PRACH resources, the UE randomly selects a PRACH preamble from the PRACH preambles corresponding to the selected SS block.
The UE selects the earliest available PRACH resource (or PRACH occasion) from the PRACH resources (or PRACH occasions) corresponding to the selected SS block.
In one embodiment, the UE randomly selects one RPACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions) corresponding to the selected SS block.
If multiple frequency division multiplexed PRACH resources (or PRACH occasions) are available within the time corresponding to the selected SS block, the UE may select the same frequency division multiplexed PRACH resource (or PRACH occasion) from the multiple available frequency division multiplexed PRACH resources (or PRACH occasions). Randomly select one PRACH resource (or PRACH occasion) with probability.

To calculate the power to transmit the PRACH, the UE estimates the pathloss based on the signal received on the selected SS block.
After transmitting Msg1, in operation 803 the UE determines whether the RAR corresponding to the Msg1 transmission (ie Msg2) was successfully received.
If the UE successfully receives the RAR, there is no need to retransmit Msg1 at operation 804 .
If the UE is unable to receive the RAR, in operation 805 the UE determines whether the maximum number of Msg1 transmissions allowed by the UE has been performed.
If the UE has not yet performed the maximum number of allowed Msg1 transmissions, the UE retransmits Msg1.
If the UE has performed the maximum number of allowed Msg1 transmissions, the UE will not retransmit Msg1.
During the retransmission, the UE determines if the signal quality of the SS block previously selected for Msg1 transmission has the highest signal quality based on recent measurements in operation 806 .
If the SS block previously selected for Msg1 transmission has the highest signal quality, the UE does not reselect the SS block.
The threshold is set by the network in system information (e.g. with PRACH settings or in RMSI) or handover commands or dedicated RRC signaling.
The UE uses the same SS block that was selected for the previous transmission for PRACH preamble and/or PRACH resource selection and pathloss estimation for retransmission (ie, the next Msg1 transmission).
During retransmission, if the signal quality of the SS block previously selected for Msg1 transmission does not have the highest signal quality, the UE reselects the SS block at operation 807 .
The UE selects the SS block with the highest signal quality among all SS blocks transmitted by the gNB.
In another embodiment, the UE selects the SS block with the highest signal quality among all SS blocks for which measurements are available.

In alternative embodiments of such methods, CSI-RS can be used instead of SS blocks.
The UE selects the CSI-RS instead of the SS block using the same procedure as described above for the SS block.
The UE selects PRACH preambles and/or PRACH resources (or PRACH occasions) from the PRACH preambles and/or PRACH resources (or PRACH occasions) corresponding to the selected CSI-RS.

≪Key point≫
The UE selects the SS block (or CSI-RS) with the highest signal quality when the random access procedure is initiated.
The SS block (or CSI-RS) for which the previously transmitted SS block (or CSI-RS) has the highest signal quality must have the highest signal quality based on the most recent measurement selected during the retransmission. , the UE reselects the SS block (or CSI-RS) between retransmissions.
The UE uses the selected SS block (or CSI-RS) for PRACH preamble and/or PRACH resource (or PRACH occasion) selection and path loss estimation for transmission of Msg1 during the random access procedure.

≪Method 5≫
Figure 9 is a flow chart illustrating UE operation for RACH transmission and retransmission based on Method 5 according to an embodiment of the present invention.

Referring to FIG. 9, at operation 901, the UE selects a suitable SS block for initial PRACH preamble transmission.
An SS block is suitable if the signal quality of the SS block is greater than a threshold 'SSBlockThreshold'.
In an embodiment, an SS block is suitable if the signal quality of the SS block is greater than or equal to a threshold 'SSBlockThreshold'.
'SSBlockThreshold' is set by the network in system information (e.g. with PRACH setting or in RMSI) or handover command or dedicated RRC signaling.
Signal quality is measured over resources of SS blocks carrying PSS and/or SSS and/or DMRS for PBCH.
Signal quality may be RSRP or RSRQ or RSSI.
If multiple SS blocks are suitable, the UE can select the SS block in one of the following manners.

The UE selects the SS block with the highest signal quality among the suitable SS blocks.
The UE selects the SS block corresponding to the earliest available RACH resource (or PRACH occasion) in time among the suitable SS blocks.
The UE randomly selects one of the SS blocks with equal probability among the appropriate SS blocks.
The UE selects any SS block among the appropriate SS blocks.

The UE may select one of the following methods based on indications from the network (which may be signaled as part of PRACH configuration in SI and/or handover commands and/or dedicated RRC signaling).
That is, select the SS block with the highest signal quality among the appropriate SS blocks, or select the SS block corresponding to the earliest available RACH resource (or PRACH occasion) in time among the appropriate SS blocks. or randomly select one of the SS blocks with the same probability among the appropriate SS blocks.

Next, at operation 902, the UE transmits a PRACH preamble (ie, Msg1) by selecting a PRACH preamble and/or PRACH resource (or PRACH occasion) corresponding to the selected SS block.

Once an SS block is associated with a PRACH preamble, the UE randomly selects a PRACH preamble from the PRACH preambles corresponding to the selected SS block.
The UE selects the earliest available PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions).
In an embodiment, the UE randomly selects one PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions).
If multiple frequency division multiplexed PRACH resources (or PRACH occasions) are available, the UE selects one PRACH resource (or PRACH occasion) with equal probability from the multiple frequency division multiplexed PRACH resources (or PRACH occasions) available. randomly select.

Once an SS block is associated with a PRACH resource (or PRACH occasion), the UE selects the earliest available PRACH resource (or PRACH occasion) from the PRACH resource (or PRACH occasion) corresponding to the selected SS block.
In one embodiment, the UE randomly selects one PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions) corresponding to the selected SS block.
If multiple frequency division multiplexed PRACH resources (or PRACH occasions) are available within the time corresponding to the selected SS block, the UE may select the same frequency division multiplexed PRACH resource (or PRACH occasion) from the multiple available frequency division multiplexed PRACH resources (or PRACH occasions). Randomly select one PRACH resource (or PRACH occasion) with probability.
The UE randomly selects a PRACH preamble from the configured set of PRACH preambles with equal probability.

Once an SS block is associated with a PRACH preamble and a PRACH resource (or PRACH occasion), the UE randomly selects a PRACH preamble from the PRACH preambles corresponding to the selected SS block.
The UE selects the earliest available PRACH resource (or PRACH occasion) from the PRACH resources (or PRACH occasions) corresponding to the selected SS block.
In one embodiment, the UE randomly selects one PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions) corresponding to the selected SS block.
If multiple frequency division multiplexed PRACH resources (or PRACH occasions) are available in the time corresponding to the selected SS block, the UE will select from the available frequency division multiplexed PRACH resources (or PRACH occasions) with equal probability. Randomly select one PRACH resource (or PRACH occasion).

To calculate the power for transmitting the PRACH, the UE estimates the pathloss based on the signal received on the selected SS block.
After transmitting Msg1, in operation 903 the UE determines whether the RAR corresponding to the Msg1 transmission (ie Msg2) was successfully received.
If the UE successfully receives the RAR, there is no need to resend Msg1 in operation 904 .
If the UE is unable to receive the RAR, then in operation 905 the UE determines whether it has performed the maximum number of Msg1 transmissions allowed by the UE.
If the UE has not yet performed the maximum number of allowed Msg1 transmissions, the UE retransmits Msg1.
If the UE has performed the maximum number of allowed Msg1 transmissions, the UE will not retransmit Msg1.
During the retransmission, the UE determines whether the signal quality of the SS block previously selected for Msg1 transmission is greater than or equal to the threshold “SSBlockThreshold” at operation 906 .
If the signal quality of the SS block previously selected for Msg1 transmission is greater than or equal to the threshold 'SSBlockThreshold', the UE will not reselect the SS block.
The threshold is set by the network in system information (e.g. with PRACH settings or in RMSI) or handover commands or dedicated RRC signaling.
The UE uses the same SS block that was selected for the previous transmission for PRACH preamble and/or PRACH resource selection and pathloss estimation for retransmission (ie, the next Msg1 transmission).
During retransmission, the UE reselects the SS block in operation 907 if the signal quality of the SS block previously selected for Msg1 transmission is less than the threshold 'SSBlockThreshold'.
The UE selects the appropriate SS block in the same manner that the UE selected the UE block for the initial Msg1 transmission.
In an alternative embodiment, during retransmission, the terminal can select SS blocks in the same manner as in the initial transmission.

With the procedure described above, the UE may not be able to find any suitable SS block.
In this case, the UE either:
UE does not send Msg1.
Additionally, the UE triggers cell reselection for idle/inactive state and RLF (ie connection reconfiguration) for connected state.

The UE selects the SS block for which measurements are available or the SS block with the highest signal quality among all SS blocks.
In this case (i.e., when no suitable SS block is selected), during the retransmission of Msg1, the UE will receive a Change the SS block.
In one embodiment, the UE is allowed to send Msg1 without selecting a suitable SS block between the 'N' number.
Parameter N is either predefined or signaled by the network.

The UE delays Msg1 transmission until the UE finds a suitable SS block.
In one embodiment, the UE may delay the Msg1 transmission for a maximum time period 'T'.
The time period T is configured by the network in system information (e.g. with PRACH configuration or in RMSI) or handover commands or dedicated RRC signaling.
After this time expires, the UE triggers cell reselection for idle/inactive state and RLF for connected state (ie, connection reconfiguration) if a suitable SS block is still not found.
Alternatively, if a suitable SS block is still not found, after this time has expired the UE has the highest signal quality among all SS blocks or among SS blocks for which measurements are available. Select the SS block.

In alternative embodiments of this method, CSI-RS can be used instead of SS blocks.
The UE selects the CSI-RS instead of the SS block using the same procedure as described above for the SS block.
The UE selects PRACH preambles and/or PRACH resources (or PRACH occasions) from the PRACH preambles and/or PRACH resources (or PRACH occasions) corresponding to the selected CSI-RS.

≪Key point≫
1) UE selects appropriate SS block (or CSI-RS) when random access procedure is initiated.
If the previously transmitted SS block (or CSI-RS) is below the threshold based on the most recent measurement selected during the retransmission of the appropriate SS block (or CSI-RS), the UE Reselect the SS block (or CSI-RS) in between.
The UE uses the PRACH preamble for transmission of Msg1 during the random access procedure and/or the selected SS block (or CSI-RS) for PRACH resource (or PRACH occasion) selection and path loss estimation.

2) If no suitable SS block is found, the UE selects the SS block (or CSI-RS) with the highest signal quality.
3) no suitable SS block (or CSI-RS) was used for the previous transmission, the SS block (or CSI-RS) for the previous transmission is still not suitable, and another suitable SS block ( or CSI-RS) is found, the UE changes the SS block (or CSI-RS).
4) If no suitable SS block (or CSI-RS) is found, the UE reselects the cell.
5) The UE delays Msg1 transmission until a suitable SS block (or CSI-RS) is found.
6) If no suitable SS block (or CSI-RS) is found, the UE delays Msg1 transmission for a defined time period.
If a suitable SS block (or CSI-RS) is not found after that time period, the UE triggers cell reselection for idle/inactive state and RLF for connected state (ie connection reconfiguration).

≪Method 6≫
FIG. 10 is a flow chart illustrating UE operation for RACH transmission and retransmission based on method 6 according to embodiments of the present invention.

Referring to Figure 10, at operation 1001, the UE selects a suitable SS block for initial PRACH preamble transmission.
An SS block is suitable if the signal quality of the SS block is greater than a threshold 'SSBlockThreshold'.
In an embodiment, an SS block is suitable if the signal quality of the SS block is greater than or equal to a threshold 'SSBlockThreshold'.
'SSBlockThreshold' is set by the network in system information (e.g. with PRACH setting or in RMSI) or handover command or dedicated RRC signaling.
Signal quality is measured over the resources of the SS blocks carrying the PSS and/or SSS and/or DMRS for the PBCH.
Signal quality may be RSRP or RSRQ or RSSI.
If multiple SS blocks are suitable, the UE can select the SS block in one of the following schemes.

The UE selects the SS block with the highest signal quality among the suitable SS blocks.
The UE selects the SS block corresponding to the earliest available RACH resource (or PRACH occasion) in time among the suitable SS blocks.
The UE randomly selects one of the SS blocks with equal probability among the appropriate SS blocks.
The UE selects any SS block among the appropriate SS blocks.

The UE may select one of the following methods based on indications from the network (which may be signaled as part of PRACH configuration in SI and/or handover commands and/or dedicated RRC signaling).
That is, select the SS block with the highest signal quality among the appropriate SS blocks, or select the SS block corresponding to the earliest available RACH resource (or PRACH occasion) in time among the appropriate SS blocks. Alternatively, one of the SS blocks can be randomly selected with the same probability among the appropriate SS blocks.

Next, at operation 1002, the UE transmits a PRACH preamble (ie, Msg1) by selecting a PRACH preamble and/or PRACH resource (or PRACH occasion) corresponding to the selected SS block.

Once an SS block is associated with a PRACH preamble, the UE randomly selects a PRACH preamble from the PRACH preambles corresponding to the selected SS block.
The UE selects the earliest available PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions).
In one embodiment, the UE randomly selects one PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions).
If multiple PRACH resources (or PRACH occasions) are available in time, the UE randomly selects one PRACH resource (or PRACH occasion) from the available PRACH resources (or PRACH occasions) with equal probability. .

Once an SS block is associated with a PRACH resource (or PRACH occasion), the UE selects the earliest available PRACH resource (or PRACH occasion) from the PRACH resource (or PRACH occasion) corresponding to the selected SS block.
In one embodiment, the UE randomly selects one PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions) corresponding to the selected SS block.
If multiple frequency division multiplexed PRACH resources (or PRACH occasions) are available in the time corresponding to the selected SS block, the UE will select one PRACH from the available PRACH resources (or PRACH occasions) with equal probability. Randomly select a resource (or PRACH occasion).
The UE randomly selects a PRACH preamble from the configured set of PRACH preambles with equal probability.

Once an SS block is associated with a PRACH preamble and a PRACH resource (or PRACH occasion), the UE randomly selects a PRACH preamble from the PRACH preambles corresponding to the selected SS block.
The UE selects the earliest available PRACH resource (or PRACH occasion) from the PRACH resources (or PRACH occasions) corresponding to the selected SS block.
In one embodiment, the UE randomly selects one PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions) corresponding to the selected SS block.
If multiple PRACH resources (or PRACH occasions) are available within the time corresponding to the selected SS block, the UE selects one PRACH resource (or PRACH occasion) is randomly selected.

To calculate the power for transmitting the PRACH, the UE estimates the pathloss based on the signal received on the selected SS block.
After transmitting Msg1, in operation 1003 the UE determines whether the RAR corresponding to the Msg1 transmission (ie Msg2) was successfully received.
If the UE successfully receives the RAR, there is no need to retransmit Msg1 at operation 1004 .
If the UE is unable to receive the RAR, then in operation 1005 the UE determines whether it has performed the maximum number of Msg1 transmissions allowed by the UE.
If the UE has not yet performed the maximum number of allowed Msg1 transmissions, the UE retransmits Msg1.
If the UE has performed the maximum number of allowed Msg1 transmissions, the UE will not retransmit Msg1.
During retransmission, the UE determines whether the signal quality of the SS block previously selected for Msg1 transmission has the best signal quality available or among all SS block measurements in operation 1006. .
If the signal quality of the SS block previously selected for Msg1 transmission has the best signal quality available or among all SS block measurements, the UE does not reselect the SS block.
Otherwise, in operation 1007, the UE reselects the appropriate SS block in the same manner that the UE selected the SS block for the initial Msg1 transmission.
In an alternative embodiment, during retransmission, the signal quality of the SS block previously selected for Msg1 transmission does not exceed 'SSBlockThreshold' and the best signal available or among all SS block measurements If not, the UE reselects the SS block in the same manner that the UE selected the SS block for the initial Msg1 transmission.
Otherwise, the UE does not reselect the SS block.
The threshold is set by the network in system information (e.g. with PRACH settings or in RMSI) or handover commands or dedicated RRC signaling.

With the procedure described above, the UE may not be able to find any suitable SS block.
In this case, the UE either:

UE does not send Msg1.
Additionally, the UE triggers cell reselection for idle/inactive state and RLF (ie connection reconfiguration) for connected state.
The UE selects the SS block for which measurements are available or the SS block with the highest signal quality among all SS blocks.
In this case (i.e., when no suitable SS block is selected), during the retransmission of Msg1, the UE will receive a Change the SS block.
In one embodiment, the UE is allowed to send Msg1 without selecting a suitable SS block between the 'N' number.
Parameter N is either predefined or signaled by the network.

The UE delays Msg1 transmission until the UE finds a suitable SS block.
In one embodiment, the UE may delay the Msg1 transmission for a maximum time period 'T'.
The time period T is configured by the network in system information (e.g. with PRACH configuration or in RMSI) or handover commands or dedicated RRC signaling.
After this time expires, the UE triggers cell reselection for idle/inactive state and RLF for connected state (ie, connection reconfiguration) if a suitable SS block is still not found.
Alternatively, if a suitable SS block is still not found, after this time has expired the UE has the highest signal quality among all SS blocks or among SS blocks for which measurements are available. Select the SS block.

In alternative embodiments of this method, CSI-RS can be used instead of SS blocks.
The UE selects the CSI-RS instead of the SS block using the same procedure as described above for the SS block.
The UE selects PRACH preambles and/or PRACH resources (or PRACH occasions) from the PRACH preambles and/or PRACH resources (or PRACH occasions) corresponding to the selected CSI-RS.

≪Key point≫
1) UE selects appropriate SS block (or CSI-RS) when random access procedure is initiated.
If the previously transmitted SS block (or CSI-RS) is not the best available SS block (or CSI-RS) measurement, the UE may repeat the SS block (or CSI-RS) between retransmissions. select.
The UE uses the PRACH preamble for transmission of Msg1 and/or the selected SS block (or CSI-RS) for PRACH resource (or PRACH occasion) selection and path loss estimation during the random access procedure.

2) UE selects appropriate SS block (or CSI-RS) when random access procedure is initiated.
If the signal quality of the SS block previously selected for Msg1 transmission is not above 'SSBlockThreshold' and does not have the best signal quality among the available or all SS block measurements, the UE shall during retransmission reselect the SS block (or CSI-RS) to
The UE uses the PRACH preamble for transmission of Msg1 and/or the selected SS block (or CSI-RS) for PRACH resource (or PRACH occasion) selection and path loss estimation during the random access procedure.

3) If no suitable SS block is found, the UE selects the SS block (or CSI-RS) with the highest signal quality.
4) no suitable SS block (or CSI-RS) was used for the previous transmission, the SS block (or CSI-RS) for the previous transmission is still not suitable, and another suitable SS block ( or CSI-RS) is found, the UE changes the SS block (or CSI-RS).
5) If no suitable SS block (or CSI-RS) is found, the UE reselects the cell.
6) UE delays Msg1 transmission until a suitable SS block (or CSI-RS) is found.
7) If no suitable SS block (or CSI-RS) is found, the UE delays Msg1 transmission for a defined time period.
If a suitable SS block (or CSI-RS) is not found after that time period, the UE triggers cell reselection for idle/inactive state and RLF for connected state (ie connection reconfiguration).

≪Method 7≫
FIG. 11 is a flow chart illustrating UE operation for RACH transmission and retransmission based on method 7 according to an embodiment of the present invention.

Referring to FIG. 11, at operation 1101, the UE selects the SS block with the highest signal quality for initial PRACH preamble transmission.
Signal quality is measured over resources of SS blocks carrying PSS and/or SSS and/or DMRS for PBCH.
Signal quality may be RSRP or RSRQ or RSSI.
In one embodiment, the UE selects the SS block with the highest signal quality among all SS blocks transmitted by the gNB.
In another embodiment, the UE selects the SS block with the highest signal quality among all SS blocks for which measurements are available.

The UE then selects PRACH preambles and/or PRACH resources (or PRACH occasions) corresponding to the selected SS block for transmitting the PRACH preamble (ie, Msg1).
At act 1102, the UE determines whether contention-free PRACH preambles and/or resources are configured for the selected SS block.
If the UE is configured with contention-free (i.e., dedicated) PRACH preambles and/or PRACH resources corresponding to the selected SS block, then at operation 1103, the UE receives dedicated PRACH preambles and/or PRACH resources corresponding to the selected block. Or select a PRACH resource.
Otherwise, at operation 1104, the UE selects a PRACH preamble corresponding to the selected SS block and/or a PRACH preamble and/or a PRACH resource corresponding to the SS block selected from the contention-based subset of PRACH resources.

Once the SS block is associated with a dedicated preamble, the UE uses that PRACH preamble.
Otherwise, the UE randomly selects a PRACH preamble from the contention-based PRACH preambles corresponding to the selected SS block.

If an SS block is associated with a dedicated PRACH resource (PRACH occasion), the UE selects a PRACH resource (PRACH occasion) from the dedicated PRACH resources, otherwise the UE selects a contention-based PRACH corresponding to the selected SS block. Select a PRACH resource (PRACH occasion) from resources (or PRACH occasions).
The UE selects the earliest available PRACH resource (PRACH occasion) from the PRACH resources (PRACH occasion) corresponding to the selected SS block (“dedicated” if available, otherwise “contention”).
In one embodiment, the UE randomly selects one PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions) corresponding to the selected SS block ("dedicated" if available). , otherwise "conflict").
If multiple frequency division multiplexed PRACH resources (PRACH occasions) are available within the time corresponding to the selected SS block, the UE will select from the available multiple frequency division multiplexed PRACH resources (PRACH occasions) with equal probability. randomly select one PRACH resource (PRACH occasion).
The UE randomly selects a PRACH preamble from the configured set of PRACH preambles with equal probability.

At operation 1105, the UE transmits Msg1 using the selected PRACH preamble and/or PRACH resources corresponding to the selected SS block.

To calculate the power for transmitting the PRACH, the UE estimates the pathloss based on the signal received on the selected SS block.
After transmitting Msg1, at operation 1106, the UE determines whether the RAR corresponding to the Msg1 transmission (ie, Msg2) was successfully received.
If the UE successfully receives the RAR, then in operation 1107 there is no need to retransmit Msg1.
If the UE is unable to receive the RAR, then at operation 1108 the UE determines whether it has performed the maximum number of Msg1 transmissions allowed by the UE.
If the UE has not yet performed the maximum number of allowed Msg1 transmissions, the UE retransmits Msg1.
If the UE has performed the maximum number of allowed Msg1 transmissions, the UE will not retransmit Msg1.
Between retransmissions, the UE does not reselect SS blocks.
The UE uses the same SS block that was selected for the initial transmission.
The SS block is selected when the random access procedure is initiated, and during the random access procedure, the PRACH preamble and/or PRACH resource (or PRACH occasion) selection and path loss estimation for any (re)transmission of Msg1. The same SS block is used for
In an alternative embodiment, during retransmissions, the terminal can select SS blocks in the same manner as in the initial transmission.

In alternative embodiments of this method, CSI-RS can be used instead of SS blocks.
The UE selects the CSI-RS instead of the SS block using the same procedure as described above for the SS block.
The UE selects PRACH preambles and/or PRACH resources (or PRACH occasions) from the PRACH preambles and/or PRACH resources (or PRACH occasions) corresponding to the selected CSI-RS.

≪Key point≫
The UE selects the SS block (or CSI-RS) with the highest signal quality.
During the random access procedure, the same SS block (or CSI-RS) is used for Msg1 (re)transmission.
The UE selects PRACH preambles and/or PRACH resources corresponding to SS blocks (or CSI-RS) selected from CF resources (if configured), otherwise the UE selects from CB resources Select PRACH preambles and/or PRACH resources corresponding to SS blocks.

≪Method 8≫
Figure 12 is a flow chart illustrating UE operation for RACH transmission and retransmission based on Method 8 according to an embodiment of the present invention.

Referring to FIG. 12, at operation 1201, the UE selects the SS block with the highest signal quality for initial PRACH preamble transmission.
Signal quality is measured via resources of SS blocks carrying PSS and/or SSS and/or DMRS for PBCH.
Signal quality may be RSRP or RSRQ or RSSI.
In this way, the UE can select the SS block with the highest signal quality among the SS blocks whose contention-free preambles and/or resources are configured for the UE by the gNB.

Next, in operation 1202, the UE selects PRACH preambles and/or PRACH resources (or PRACH occasions) corresponding to the selected SS block, and in operation 1203, the UE selects the selection corresponding to the selected SS block. Msg1 is transmitted using the designated PRACH preamble and/or PRACH resource.

Once the SS block is associated with a dedicated preamble, the UE uses that PRACH preamble.
Otherwise, the UE randomly selects a PRACH preamble from the contention-based PRACH preambles corresponding to the selected SS block.

If the SS block is associated with a dedicated PRACH resource (or PRACH occasion), the UE selects the PRACH resource (or PRACH occasion) from the dedicated PRACH resource, otherwise the UE has a contention corresponding to the selected SS block. Select PRACH resources (or PRACH occasions) from underlying PRACH resources (or PRACH occasions).
The UE selects the earliest available PRACH resource (or PRACH occasion) from the PRACH resources (or PRACH occasions) corresponding to the selected SS block (“dedicated” if available, otherwise “conflict”). ).
In one embodiment, the UE randomly selects one PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions) corresponding to the selected SS block ("dedicated" if available). , otherwise "conflict").
If multiple frequency division multiplexed PRACH resources (or PRACH occasions) are available within the time corresponding to the selected SS block, the UE can select the same frequency division multiplexed PRACH resource (or PRACH occasion) from the available multiple frequency division multiplexed PRACH resources (or PRACH occasions). Randomly select one PRACH resource (or PRACH occasion) with a probability of .
The UE randomly selects a PRACH preamble from the configured set of PRACH preambles with equal probability.

To calculate the power for transmitting the PRACH, the UE estimates the pathloss based on the signal received on the selected SS block.
After transmitting Msg1, at operation 1204, the UE determines whether the RAR corresponding to the Msg1 transmission (ie, Msg2) was successfully received.
If the UE successfully receives the RAR, then at operation 1205 there is no need to retransmit Msg1.
If the UE is unable to receive the RAR, then at operation 1206 the UE determines whether it has performed the maximum number of Msg1 transmissions allowed by the UE.
If the UE has not yet performed the maximum number of allowed Msg1 transmissions, the UE retransmits Msg1.
If the UE has performed the maximum number of allowed Msg1 transmissions, the UE will not retransmit Msg1.
Between retransmissions, the UE does not reselect SS blocks.
The UE uses the same SS block that was selected for the initial transmission.
The SS block is selected when the random access procedure is initiated, for PRACH preamble and/or PRACH resource (or PRACH occasion) selection and pathloss estimation for any (re)transmission of Msg1 during the random access procedure. The same SS block is used for
In an alternative embodiment, during retransmission, the terminal can select SS blocks in the same manner as in the initial transmission.

In alternative embodiments of this method, CSI-RS can be used instead of SS blocks.
The UE selects the CSI-RS instead of the SS block using the same procedure as described above for the SS block.
The UE selects PRACH preambles and/or PRACH resources (or PRACH occasions) from the PRACH preambles and/or PRACH resources (or PRACH occasions) corresponding to the selected CSI-RS.

≪Key point≫
The UE selects the SS block (or CSI-RS) with the highest signal quality among the SS blocks (or CSI-RS) for which contention-free preambles and/or resources are provided to the UE.
During the random access procedure, the same SS block (or CSI-RS) is used for Msg1 (re)transmission.
The UE selects at least one of PRACH preambles and/or PRACH resources corresponding to the SS block (or CSI-RS) selected from the CF source.

≪Method 9≫
Figure 13 is a flow chart illustrating UE operation for RACH transmission and retransmission based on Method 9 according to an embodiment of the present invention.

Referring to Figure 13, at operation 1301, the UE selects a suitable SS block for initial PRACH preamble transmission.
An SS block is suitable if the signal quality of the SS block is greater than a threshold 'SSBlockThreshold'.
In an embodiment, an SS block is suitable if the signal quality of the SS block is greater than or equal to a threshold 'SSBlockThreshold'.
'SSBlockThreshold' is set by the network in system information (e.g. with PRACH setting or in RMSI) or handover command or dedicated RRC signaling.
Signal quality is measured over resources of SS blocks carrying PSS and/or SSS and/or DMRS for PBCH.
Signal quality may be RSRP or RSRQ or RSSI.
If multiple SS blocks are suitable, the UE can select the SS block in one of the following schemes.

The UE selects the SS block with the highest signal quality among the suitable SS blocks.
The UE selects the SS block corresponding to the earliest available RACH resource (or PRACH occasion) in time among the suitable SS blocks.
The UE randomly selects one of the SS blocks with equal probability among the appropriate SS blocks.
The UE selects any SS block among the appropriate SS blocks.

The UE may select one of the following methods based on indications from the network (which may be signaled as part of PRACH configuration in SI and/or handover commands and/or dedicated RRC signaling).
That is, select the SS block with the highest signal quality among the appropriate SS blocks, or select the SS block corresponding to the earliest available RACH resource (or PRACH occasion) in time among the appropriate SS blocks. or randomly select one of the SS blocks with the same probability among the appropriate SS blocks.

The UE then selects PRACH preambles and/or PRACH resources (or PRACH occasions) corresponding to the selected SS block for transmitting the PRACH preamble (ie, Msg1).
At operation 1302, the UE determines whether contention-free PRACH preambles and/or resources are configured for the selected SS block.
Once the UE is configured with a contention-free (i.e., dedicated) PRACH preamble and/or PRACH resource corresponding to the selected SS block, at operation 1303, the UE may receive a dedicated PRACH preamble and/or PRACH resource corresponding to the selected block. Select a PRACH resource.
Otherwise, at operation 1304, the UE selects a PRACH preamble corresponding to the selected SS block and/or a PRACH preamble and/or a PRACH resource corresponding to the SS block selected from the contention-based subset of PRACH resources.

Once the SS block is associated with a dedicated preamble, the UE uses that PRACH preamble.
Otherwise, the UE randomly selects a PRACH preamble from the contention-based PRACH preambles corresponding to the selected SS block.

If the SS block is associated with a dedicated PRACH resource (or PRACH occasion), the UE selects the PRACH resource (or PRACH occasion) from the dedicated PRACH resource, otherwise the UE has a contention corresponding to the selected SS block. Select PRACH resources (or PRACH occasions) from underlying PRACH resources (or PRACH occasions).
The UE selects the earliest available PRACH resource (or PRACH occasion) from the PRACH resources (or PRACH occasions) corresponding to the selected SS block (“dedicated” if available, otherwise “conflict”). ). In embodiments, the UE may randomly select one PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions) corresponding to the selected SS block ("dedicated" if available). ", otherwise "conflict").
If multiple frequency division multiplexed PRACH resources (or PRACH occasions) are available within the time corresponding to the selected SS block, the UE can select the same frequency division multiplexed PRACH resource (or PRACH occasion) from the available multiple frequency division multiplexed PRACH resources (or PRACH occasions). Randomly select one PRACH resource (or PRACH occasion) with a probability of .
The UE randomly selects a PRACH preamble from the configured set of PRACH preambles with equal probability.

At operation 1305, the UE transmits Msg1 using the selected PRACH preamble and/or PRACH resources corresponding to the selected SS block.

To calculate the power for transmitting the PRACH, the UE estimates the pathloss based on the signal received on the selected SS block.
After transmitting Msg1, at operation 1306 the UE determines whether the RAR corresponding to the Msg1 transmission (ie, Msg2) was successfully received.
If the UE successfully receives the RAR, then in operation 1307 there is no need to retransmit Msg1.
If the UE is unable to receive the RAR, then at operation 1308 the UE determines whether it has performed the maximum number of Msg1 transmissions allowed by the UE.
If the UE has not yet performed the maximum number of allowed Msg1 transmissions, the UE retransmits Msg1.
If the UE has performed the maximum number of allowed Msg1 transmissions, the UE will not retransmit Msg1.
Between retransmissions, the UE does not reselect SS blocks.
The UE uses the same SS block that was selected for the initial transmission.
The appropriate SS block is selected when the random access procedure is initiated, and is used for PRACH preamble and/or PRACH resource (or PRACH occasion) selection and path loss estimation for any (re)transmission of Msg1 during the random access procedure. The same SS block is used for
If no suitable SS block is found, the UE reselects a suitable SS block between retransmissions as described below.

With the procedure described above, the UE may not be able to find any suitable SS block.
In this case, the UE either:

UE does not send Msg1.
Additionally, the UE triggers cell reselection for idle/inactive state and RLF (ie connection reconfiguration) for connected state.

The UE selects the SS block for which measurements are available or the SS block with the highest signal quality among all SS blocks.
In this case (i.e., when no suitable SS block is selected), during the retransmission of Msg1, the UE will receive a Change the SS block.
In one embodiment, the UE may be allowed to send Msg1 without selecting a suitable SS block between the 'N' number.
Parameter N is either predefined or signaled by the network.

The UE delays Msg1 transmission until the UE finds a suitable SS block.
In one embodiment, the UE may delay the Msg1 transmission for a maximum time period 'T'.
The time period T is configured by the network in system information (e.g. with PRACH configuration or in RMSI) or handover commands or dedicated RRC signaling.
After this time expires, the UE triggers cell reselection for idle/inactive state and RLF for connected state (ie, connection reconfiguration) if a suitable SS block is still not found.
Alternatively, if a suitable SS block is still not found, after this time has expired the UE has the highest signal quality among all SS blocks or among SS blocks for which measurements are available. Select the SS block.
In an alternative embodiment, during retransmissions the terminal can select SS blocks in the same manner as in the initial transmission.

As an alternative embodiment of this method, CSI-RS can be used instead of SS blocks.
The UE selects the CSI-RS instead of the SS block using the same procedure as described above for the SS block.
The UE selects PRACH preambles and/or PRACH resources (or PRACH occasions) from the PRACH preambles and/or PRACH resources (or PRACH occasions) corresponding to the selected CSI-RS.

≪Key point≫
1) The UE selects a suitable (signal quality>SSBlockThreshold) SS block (or CSI-RS) when the random access procedure is initiated.
The UE uses the selected SS block (or CSI-RS) for PRACH preamble and/or PRACH resource (or PRACH occasion) selection and path loss estimation for every (re)transmission of Msg1 during the random access procedure .
Contention-free PRACH preambles and/or PRACH resources (or PRACH occasions) for the selected SS block are selected when available.
Otherwise, a contention-based PRACH preamble and/or PRACH resource for the selected SS block is selected.

2) If no suitable SS block is found, the UE selects the SS block (or CSI-RS) with the highest signal quality.
3) no suitable SS block (or CSI-RS) was used for the previous transmission, the SS block (or CSI-RS) for the previous transmission is still not suitable, and another suitable SS block ( or CSI-RS) is found, the UE changes the SS block (or CSI-RS).

4) If no suitable SS block (or CSI-RS) is found, the UE reselects the cell.
5) The UE delays Msg1 transmission until a suitable SS block (or CSI-RS) is found.
6) If no suitable SS block (or CSI-RS) is found, the UE delays Msg1 transmission for a defined time period.
If no suitable SS block (or CSI-RS) is found after that time period, the UE triggers cell reselection for idle/inactive state and RLF for connected state (ie connection reconfiguration).

≪Method 10≫
FIG. 14 is a flow chart illustrating UE operation for RACH transmission and retransmission based on method 10 according to embodiments of the present invention.

Referring to Figure 14, at operation 1401, the UE selects a suitable SS block for initial PRACH preamble transmission.
An SS block is suitable if the signal quality of the SS block is greater than a threshold 'SSBlockThreshold'.
In an embodiment, an SS block is suitable if the signal quality of the SS block is greater than or equal to a threshold 'SSBlockThreshold'.
'SSBlockThreshold' is set by the network in system information (e.g. with PRACH setting or in RMSI) or handover command or dedicated RRC signaling.
Signal quality is measured over resources of SS blocks carrying PSS and/or SSS and/or DMRS for PBCH.
Signal quality may be RSRP or RSRQ or RSSI.

In operation 1402 of this method, the UE first checks whether there is a suitable SS block among the SS blocks for which dedicated PRACH preambles and/or PRACH resources are configured.
Once a suitable SS block for which dedicated PRACH preambles and/or PRACH resources are configured is found, the UE selects that SS block and assigns dedicated PRACH preambles and/or PRACH resources corresponding to the SS block selected in operation 1403. to select.
If multiple SS blocks are suitable SS blocks for which dedicated preambles and/or resources are configured, the UE may select the SS blocks in one of the following schemes.

The UE selects the SS block with the highest signal quality among the suitable SS blocks.
The UE selects the SS block corresponding to the earliest available RACH resource (or PRACH occasion) in time among the suitable SS blocks.
The UE randomly selects one of the SS blocks with equal probability among the appropriate SS blocks.
The UE selects any SS block among the appropriate SS blocks.

The UE may select one of the following methods based on indications from the network (which may be signaled as part of PRACH configuration in SI and/or handover commands and/or dedicated RRC signaling).
That is, select the SS block with the highest signal quality among the appropriate SS blocks, or select the SS block corresponding to the earliest available RACH resource (or PRACH occasion) in time among the appropriate SS blocks. or randomly select one of the SS blocks with the same probability among the appropriate SS blocks.

If no suitable SS block is found in the SS block for which dedicated PRACH preambles and/or PRACH resources are configured, then at operation 1404 the UE selects a suitable SS block for which contention-based preambles and/or resources are configured. Having selected a block, at operation 1405 the UE selects a contention-based PRACH preamble and/or PRACH resource corresponding to the selected SS block.
When multiple SS blocks are suitable SS blocks for which contention-based preambles and/or resources are configured, the UE may select the SS block in one of the following schemes.

The UE selects the SS block with the highest signal quality among the suitable SS blocks.
The UE selects the SS block corresponding to the earliest available RACH resource (or PRACH occasion) in time among the suitable SS blocks.
The UE randomly selects one of the SS blocks with equal probability among the appropriate SS blocks.
The UE selects any SS block among the appropriate SS blocks.

The UE may select one of the following methods based on indication from the network (which may be signaled as part of PRACH configuration in SI and/or handover command and/or dedicated RRC signaling).
That is, select the SS block with the highest signal quality among the appropriate SS blocks, or select the SS block corresponding to the earliest available RACH resource (or PRACH occasion) in time among the appropriate SS blocks. or randomly select one of the SS blocks with the same probability among the appropriate SS blocks.

Next, at operation 1406, the UE transmits a PRACH preamble (ie, Msg1) using the selected PRACH preamble and/or PRACH resources corresponding to the selected SS block.

Once the SS block is associated with a dedicated preamble, the UE uses that PRACH preamble.
Otherwise, the UE randomly selects a PRACH preamble from the contention-based PRACH preambles corresponding to the selected SS block.

If the SS block is associated with a dedicated PRACH resource (or PRACH occasion), the UE selects the PRACH resource (or PRACH occasion) from the dedicated PRACH resource, otherwise the UE has a contention corresponding to the selected SS block. Select PRACH resources (or PRACH occasions) from underlying PRACH resources (or PRACH occasions).
The UE selects the earliest available PRACH resource (or PRACH occasion) from the PRACH resources (or PRACH occasions) corresponding to the selected SS block (“dedicated” if available, otherwise “conflict”). ).
In one embodiment, the UE randomly selects one PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions) corresponding to the selected SS block ("dedicated" if available). , otherwise "conflict").
If multiple frequency division multiplexed PRACH resources (or PRACH occasions) are available within the time corresponding to the selected SS block, the UE can select the same frequency division multiplexed PRACH resource (or PRACH occasion) from the available multiple frequency division multiplexed PRACH resources (or PRACH occasions). Randomly select one PRACH resource (or PRACH occasion) with a probability of .
The UE randomly selects a PRACH preamble from the configured set of PRACH preambles with equal probability.

To calculate the power for transmitting the PRACH, the UE estimates the pathloss based on the signal received on the selected SS block.
After transmitting Msg1, in operation 1407 the UE determines whether the RAR corresponding to the Msg1 transmission (ie Msg2) was successfully received.
If the UE successfully receives the RAR, then at operation 1408 there is no need to retransmit Msg1.
If the UE is unable to receive the RAR, then in operation 1409 the UE determines whether it has performed the maximum number of Msg1 transmissions allowed by the UE.
If the UE has not yet performed the maximum number of allowed Msg1 transmissions, the UE retransmits Msg1.
If the UE has performed the maximum number of allowed Msg1 transmissions, the UE will not retransmit Msg1.
Between retransmissions, the UE does not reselect SS blocks.
The UE uses the same SS block that was selected for the initial transmission.
The appropriate SS block is selected when the random access procedure is initiated, PRACH preamble and/or PRACH resource (or PRACH occasion) selection and pathloss estimation for any (re)transmission of Msg1 during the random access procedure. The same SS block is used for
If no suitable SS block is found, the UE reselects a suitable SS block during retransmission, as described below.
In an alternative embodiment, during retransmissions, the terminal can select SS blocks in the same manner as in the initial transmission.

With the procedure described above, the UE may not be able to find any suitable SS block while selecting the SS block corresponding to the contention-based preamble and/or resources.
In this case, the UE either:

UE does not send Msg1.
Additionally, the UE triggers cell reselection for idle/inactive state and RLF (ie connection reconfiguration) for connected state.

The UE selects the SS block for which measurements are available or the SS block with the highest signal quality among all SS blocks.
In this case (i.e., when no suitable SS block is selected), during the retransmission of Msg1, the UE will receive , change the SS block.
In one embodiment, the UE is allowed to send Msg1 without selecting a suitable SS block between the 'N' number.
Parameter N is either predefined or signaled by the network.

The UE delays Msg1 transmission until the UE finds a suitable SS block.
In one embodiment, the UE may delay the Msg1 transmission for a maximum time period 'T'.
The time period T is configured by the network in system information (e.g. with PRACH configuration or in RMSI) or handover commands or dedicated RRC signaling.
After this time expires, the UE triggers cell reselection for idle/inactive state and RLF for connected state (ie, connection reconfiguration) if a suitable SS block is still not found.
Alternatively, if a suitable SS block is still not found, after this time has expired the UE has the highest signal quality among all SS blocks or among SS blocks for which measurements are available. Select the SS block.

As an alternative embodiment of this method, CSI-RS can be used instead of SS blocks.
The UE selects the CSI-RS instead of the SS block using the same procedure as described above for the SS block.
The UE selects PRACH preambles and/or PRACH resources (or PRACH occasions) from the PRACH preambles and/or PRACH resources (or PRACH occasions) corresponding to the selected CSI-RS.

≪Key point≫
1) The UE selects an appropriate SS block (or CSI-RS) from SS blocks (or CSI-RS) in which CF resources are configured.
If a suitable SS block (or CSI-RS) is not found from the SS block (or CSI-RS) where CF resources are configured, the UE finds a suitable SS block (or CSI-RS) where CB resources are configured. SS block (or CSI-RS) is selected.
UE selects SS block (or CSI-RS) for PRACH preamble and/or PRACH resource (or PRACH occasion) selection and path loss estimation for every (re)transmission of Msg1 during random access procedure Use

2) If no suitable SS block is found, the UE selects the SS block (or CSI-RS) with the highest signal quality.
3) no suitable SS block (or CSI-RS) was used for the previous transmission, the SS block (or CSI-RS) for the previous transmission is still not suitable, and another suitable SS block ( or CSI-RS) is found, the UE changes the SS block (or CSI-RS).
4) If no suitable SS block (or CSI-RS) is found, the UE reselects the cell.
5) The UE delays Msg1 transmission until a suitable SS block (or CSI-RS) is found.
6) If no suitable SS block (or CSI-RS) is found, the UE delays Msg1 transmission for a defined time period.
If a suitable SS block (or CSI-RS) is not found after that time period, the UE triggers cell reselection for idle/inactive state and RLF for connected state (ie connection reconfiguration).

≪Method 11≫
Figure 15 is a flow chart illustrating UE operation for RACH transmission and retransmission based on method 11 according to an embodiment of the present invention.

Referring to Figure 15, at operation 1501, the UE selects a suitable SS block for initial PRACH preamble transmission.
An SS block is suitable if the signal quality of the SS block is greater than a threshold 'SSBlockThreshold'.
In an embodiment, an SS block is suitable if the signal quality of the SS block is greater than or equal to a threshold 'SSBlockThreshold'.
'SSBlockThreshold' is set by the network in system information (e.g. with PRACH setting or in RMSI) or handover command or dedicated RRC signaling.
Signal quality is measured via resources of SS blocks carrying PSS and/or SSS and/or DMRS for PBCH.
Signal quality may be RSRP or RSRQ or RSSI.

In operation 1502 of this method, the UE first checks whether there is a suitable SS block among the SS blocks for which dedicated PRACH preambles and/or PRACH resources are configured.
Once a suitable SS block for which dedicated PRACH preambles and/or PRACH resources are configured is found, the UE selects that SS block and assigns dedicated PRACH preambles and/or PRACH resources corresponding to the selected SS block in operation 1504. to select.
If multiple SS blocks are suitable SS blocks for which dedicated preambles and/or resources are configured, the UE may select the SS blocks in one of the following schemes.

The UE selects the SS block with the highest signal quality among the suitable SS blocks.
The UE selects the SS block corresponding to the earliest available RACH resource (or PRACH occasion) in time among the suitable SS blocks.
The UE randomly selects one of the SS blocks with equal probability among the appropriate SS blocks.
The UE selects any SS block among the appropriate SS blocks.

The UE may select one of the following methods based on indications from the network (which may be signaled as part of PRACH configuration in SI and/or handover commands and/or dedicated RRC signaling).
That is, select the SS block with the highest signal quality among the appropriate SS blocks, or select the SS block corresponding to the earliest available RACH resource (or PRACH occasion) in time among the appropriate SS blocks. or randomly select one of the SS blocks with the same probability among the appropriate SS blocks.

If no suitable SS block is found among the SS blocks in which dedicated PRACH preambles and/or PRACH resources are configured, the UE, in operation 1503, selects the most Select SS blocks with high signal quality and select dedicated PRACH preambles and/or PRACH resources corresponding to the PR blocks selected in act 1504 .

Next, at operation 1505, the UE transmits a PRACH preamble (ie, Msg1) using the selected PRACH preamble and/or PRACH resources corresponding to the selected SS block.

Once the SS block is associated with a dedicated preamble, the UE uses that PRACH preamble.
Otherwise, the UE randomly selects a PRACH preamble from the contention-based PRACH preamble set corresponding to the selected SS block.

If the SS block is associated with a dedicated PRACH resource (or PRACH occasion), the UE selects the PRACH resource (or PRACH occasion) from the dedicated PRACH, otherwise the UE selects the contention-based PRACH corresponding to the selected SS block. Select PRACH resources (or PRACH occasions) from resources (or PRACH occasions).
The UE selects the earliest available PRACH resource (or PRACH occasion) from the PRACH resources (or PRACH occasions) corresponding to the selected SS block (“dedicated” if available, otherwise “conflict”). ).
In one embodiment, the UE randomly selects one PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions) corresponding to the selected SS block ("dedicated" if available). , otherwise "conflict").
If multiple frequency division multiplexed PRACH resources (or PRACH occasions) are available within the time corresponding to the selected SS block, the UE can select the same frequency division multiplexed PRACH resource (or PRACH occasion) from the available multiple frequency division multiplexed PRACH resources (or PRACH occasions). Randomly select one PRACH resource (or PRACH occasion) with a probability of .
The UE randomly selects a PRACH preamble from the configured set of PRACH preambles with equal probability.

To calculate the power for transmitting the PRACH, the UE estimates the pathloss based on the signal received on the selected SS block.
After transmitting Msg1, at operation 1506 the UE determines whether the RAR corresponding to the Msg1 transmission (ie, Msg2) was successfully received.
If the UE successfully receives the RAR, then in operation 1507 there is no need to retransmit Msg1.
If the UE is unable to receive the RAR, then at operation 1508 the UE determines whether it has performed the maximum number of Msg1 transmissions allowed by the UE.
If the UE has not yet performed the maximum number of allowed Msg1 transmissions, the UE retransmits Msg1.
If the UE has performed the maximum number of allowed Msg1 transmissions, the UE will not retransmit Msg1.
Between retransmissions, the UE does not reselect SS blocks.
The UE uses the same SS block that was selected for the initial transmission.
The appropriate SS block is selected when the random access procedure is initiated, and is used for PRACH preamble and/or PRACH resource (or PRACH occasion) selection and path loss estimation for any (re)transmission of Msg1 during the random access procedure. The same SS block is used for
As an alternative embodiment, during the retransmission the terminal can select the SS block in the same manner as the initial transmission.

As an alternative embodiment of this method, CSI-RS can be used instead of SS blocks.
The UE selects the CSI-RS instead of the SS block using the same procedure as described above for the SS block.
The UE selects PRACH preambles and/or PRACH resources (or PRACH occasions) from the PRACH preambles and/or PRACH resources (or PRACH occasions) corresponding to the selected CSI-RS.

≪Key point≫
The UE selects an appropriate SS block (or CSI-RS) from SS blocks (or CSI-RS) in which CF resources are configured.
If a suitable SS block (or CSI-RS) is not found from the SS block (or CSI-RS) where CF resources are configured, the UE selects the most from the SS block (or CSI-RS) where CF resources are configured. Select SS blocks (or CSI-RS) with high signal quality.
UE selects SS block (or CSI-RS) for PRACH preamble and/or PRACH resource (or PRACH occasion) selection and path loss estimation for every (re)transmission of Msg1 during random access procedure Use

≪Method 12≫
FIG. 16 is a flow chart illustrating UE operation for RACH transmission and retransmission based on method 12 according to embodiments of the present invention.

Referring to Figure 16, at operation 1601, the UE selects the SS block with the highest signal quality for initial PRACH preamble transmission.
Signal quality is measured over resources of SS blocks carrying PSS and/or SSS and/or DMRS for PBCH.
Signal quality may be RSRP or RSRQ or RSSI.
In one embodiment, the UE selects the SS block with the highest signal quality among all SS blocks transmitted by the gNB.
In another embodiment, the UE selects the SS block with the highest signal quality among all SS blocks for which measurements are available.

The UE then selects PRACH preambles and/or PRACH resources (or PRACH occasions) corresponding to the selected SS block for transmitting the PRACH preamble (ie, Msg1).
At operation 1602, the UE determines whether contention-free PRACH preambles and/or resources are configured for the selected SS block.
Once the UE is configured with a contention-free (i.e., dedicated) PRACH preamble and/or PRACH resource corresponding to the selected SS block, at operation 1603, the UE may receive a dedicated PRACH preamble and/or PRACH resource corresponding to the selected block. Select a PRACH resource.
Otherwise, at operation 1604, the UE selects a PRACH preamble corresponding to the selected SS block and/or a PRACH preamble and/or a PRACH resource corresponding to the SS block selected from the contention-based subset of PRACH resources.

Once the SS block is associated with a dedicated preamble, the UE uses that PRACH preamble.
Otherwise, the UE randomly selects a PRACH preamble from the contention-based PRACH preambles corresponding to the selected SS block.

If the SS block is associated with a dedicated PRACH resource (or PRACH occasion), the UE selects the PRACH resource (or PRACH occasion) from the dedicated PRACH resource, otherwise the UE has a contention corresponding to the selected SS block. Select PRACH resources (or PRACH occasions) from underlying PRACH resources (or PRACH occasions).
The UE selects the earliest available PRACH resource (or PRACH occasion) from the PRACH resources (or PRACH occasions) corresponding to the selected SS block (“dedicated” if available, otherwise “conflict”). ).
In one embodiment, the UE randomly selects one PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions) corresponding to the selected SS block ("dedicated" if available). , otherwise "conflict").
If multiple frequency division multiplexed PRACH resources (or PRACH occasions) are available within the time corresponding to the selected SS block, the UE can select the same frequency division multiplexed PRACH resource (or PRACH occasion) from the available multiple frequency division multiplexed PRACH resources (or PRACH occasions). Randomly select one PRACH resource (or PRACH occasion) with a probability of .
The UE randomly selects a PRACH preamble from the configured set of PRACH preambles with equal probability.

At operation 1605, the UE transmits Msg1 using the selected PRACH preamble and/or PRACH resources corresponding to the selected SS block.

To calculate the power for transmitting the PRACH, the UE estimates the pathloss based on the signal received on the selected SS block.
After transmitting Msg1, at operation 1606 the UE determines whether the RAR corresponding to the Msg1 transmission (ie, Msg2) was successfully received.
If the UE successfully receives the RAR, then in operation 1607 there is no need to retransmit Msg1.
If the UE is unable to receive the RAR, then at operation 1608 the UE determines whether it has performed the maximum number of Msg1 transmissions allowed by the UE.
If the UE has not yet performed the maximum number of allowed Msg1 transmissions, the UE retransmits Msg1.
If the UE has performed the maximum number of allowed Msg1 transmissions, the UE will not retransmit Msg1.
During retransmission, at operation 1609, the UE determines whether the signal quality of the SS block previously selected for Msg1 transmission is greater than or equal to the threshold 'SSBlockThreshold'.
If the signal quality of the SS block previously selected for Msg1 transmission is greater than or equal to the threshold 'SSBlockThreshold', the UE will not reselect the SS block.
The threshold is set by the network in system information (e.g. with PRACH settings or in RMSI) or handover commands or dedicated RRC signaling.
The UE uses the same SS block that was selected for the previous transmission for PRACH preamble and/or PRACH resource selection and path loss estimation for retransmission (ie, the next Msg1 transmission).
During retransmission, if the signal quality of the SS block previously selected for Msg1 transmission is less than the threshold 'SSBlockThreshold', the UE reselects the SS block at operation 1610 .
The UE selects the SS block with the highest signal quality among all SS blocks transmitted by the gNB.
Alternatively, the UE selects the SS block with the highest signal quality among all SS blocks for which measurements are available.
As an alternative embodiment, during retransmissions, the terminal selects SS blocks in the same manner as the initial transmission.

As an alternative embodiment of this method, CSI-RS can be used instead of SS blocks.
The UE selects the CSI-RS instead of the SS block using the same procedure as described above for the SS block.
The UE selects PRACH preambles and/or PRACH resources (or PRACH occasions) from the PRACH preambles and/or PRACH resources (or PRACH occasions) corresponding to the selected CSI-RS.

≪Key point≫
1) The UE selects the SS block (or CSI-RS) with the highest signal quality when the random access procedure is initiated.
If the SS block (or CSI-RS) of the previous transmission is below the threshold, based on recent measurements, the SS block (or CSI-RS) with the highest signal quality is selected during retransmission, The UE reselects the SS block (or CSI-RS) between retransmissions.
The UE uses the PRACH preamble for transmission of Msg1 during the random access procedure and/or the selected SS block (or CSI-RS) for PRACH resource (or PRACH occasion) selection and path loss estimation.
2) UE selects PRACH preamble and/or PRACH resource corresponding to selected SS block (or CSI-RS) from CF resource (if configured), otherwise UE selects from CB resource Select PRACH preambles and/or PRACH resources corresponding to the selected SS blocks.

≪Method 13≫
Figure 17 is a flow chart illustrating UE operation for RACH transmission and retransmission based on method 13 according to an embodiment of the present invention.

Referring to Figure 17, at operation 1701, the UE selects the SS block with the highest signal quality for initial PRACH preamble transmission.
Signal quality is measured via resources of SS blocks carrying PSS and/or SSS and/or DMRS for PBCH.
Signal quality may be RSRP or RSRQ or RSSI.
In one embodiment, the UE selects the SS block with the highest signal quality among all SS blocks transmitted by the gNB.
In another embodiment, the UE selects the SS block with the highest signal quality among all SS blocks for which measurements are available.

The UE then selects PRACH preambles and/or PRACH resources (or PRACH occasions) corresponding to the selected SS block for transmitting the PRACH preamble (ie, Msg1).
At operation 1702, the UE determines whether contention-free PRACH preambles and/or resources are configured for the selected SS block.
Once the UE is configured with a contention-free (i.e., dedicated) PRACH preamble and/or PRACH resource corresponding to the selected SS block, at operation 1703, the UE may receive a dedicated PRACH preamble and/or PRACH resource corresponding to the selected block. Select a PRACH resource.
Otherwise, at operation 1704, the UE selects a PRACH preamble corresponding to the selected SS block and/or a PRACH preamble and/or a PRACH resource corresponding to the SS block selected from the contention-based subset of PRACH resources.

Once the SS block is associated with a dedicated preamble, the UE uses that PRACH preamble.
Otherwise, the UE randomly selects a PRACH preamble from the contention-based PRACH preambles corresponding to the selected SS block.

If the SS block is associated with a dedicated PRACH resource (or PRACH occasion), the UE selects the PRACH resource (or PRACH occasion) from the dedicated PRACH resource, otherwise the UE has a contention corresponding to the selected SS block. Select a PRACH resource (PRACH occasion) from the underlying PRACH resource (or PRACH occasion).
The UE selects the earliest available PRACH resource (or PRACH occasion) from the PRACH resources (or PRACH occasions) corresponding to the selected SS block (“dedicated” if available, otherwise “conflict”). ).
In one embodiment, the UE randomly selects one PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions) corresponding to the selected SS block ("dedicated" if available). , otherwise "conflict").
If multiple frequency division multiplexed PRACH resources (or PRACH occasions) are available within the time corresponding to the selected SS block, the UE can select the same frequency division multiplexed PRACH resource (or PRACH occasion) from the available multiple frequency division multiplexed PRACH resources (or PRACH occasions). Randomly select one PRACH resource (or PRACH occasion) with a probability of .
The UE randomly selects a PRACH preamble from the configured set of PRACH preambles with equal probability.

At operation 1705, the UE transmits Msg1 using the selected PRACH preamble and/or PRACH resources corresponding to the selected SS block.

To calculate the power for transmitting the PRACH, the UE estimates the pathloss based on the signal received on the selected SS block.
After transmitting Msg1, in operation 1706 the UE determines whether the RAR corresponding to the Msg1 transmission (ie Msg2) was successfully received.
If the UE successfully receives the RAR, then in operation 1707 there is no need to retransmit Msg1.
If the UE is unable to receive the RAR, then at operation 1708 the UE determines whether it has performed the maximum number of Msg1 transmissions allowed by the UE.
If the UE has not yet performed the maximum number of allowed Msg1 transmissions, the UE retransmits Msg1.
If the UE has performed the maximum number of allowed Msg1 transmissions, the UE will not retransmit Msg1.
During retransmission, at operation 1709, the UE determines whether the signal quality of the SS block previously selected for Msg1 transmission still has the highest signal quality based on recent measurements.
If the SS block previously selected for Msg1 transmission has the highest signal quality, the UE does not reselect the SS block.
The threshold is set by the network in system information (e.g. with PRACH settings or in RMSI) or handover commands or dedicated RRC signaling.
The UE uses the same SS block that was selected for the previous transmission for PRACH preamble and/or PRACH resource selection and pathloss estimation for retransmission (ie, the next Msg1 transmission).
During retransmission, if the signal quality of the SS block previously selected for Msg1 transmission does not have the highest signal quality, the UE at operation 1710 reselects the SS block.
The UE selects the SS block with the highest signal quality among all SS blocks transmitted by the gNB.
Alternatively, the UE selects the SS block with the highest signal quality among all SS blocks for which measurements are available.
As an alternative embodiment, during retransmissions, the terminal selects SS blocks in the same manner as the initial transmission.

As an alternative embodiment of this method, CSI-RS can be used instead of SS blocks.
The UE selects the CSI-RS instead of the SS block using the same procedure as described above for the SS block.
The UE selects PRACH preambles and/or PRACH resources (or PRACH occasions) from the PRACH preambles and/or PRACH resources (or PRACH occasions) corresponding to the selected CSI-RS.

≪Key point≫
1) The UE selects the SS block (or CSI-RS) with the highest signal quality when the random access procedure is initiated.
The SS block (or CSI-RS) of the previous transmission has the highest signal quality, unless the SS block (or CSI-RS) has the highest signal quality based on the most recent measurements selected during retransmission, The UE reselects the SS block (or CSI-RS) between retransmissions.
The UE uses the PRACH preamble for transmission of Msg1 during the random access procedure and/or the selected SS block (or CSI-RS) for PRACH resource (or PRACH occasion) selection and path loss estimation.
2) UE selects PRACH preamble and/or PRACH resource corresponding to selected SS block (or CSI-RS) from CF resource (if configured), otherwise UE selects from CB resource Select PRACH preambles and/or PRACH resources corresponding to the selected SS blocks.

≪Method 14≫
FIG. 18 is a flow chart illustrating UE operation for RACH transmission and retransmission based on method 14 according to embodiments of the present invention.

Referring to Figure 18, at operation 1801, the UE selects the SS block with the highest signal quality for initial PRACH preamble transmission.
Signal quality is measured over resources of SS blocks carrying PSS and/or SSS and/or DMRS for PBCH.
Signal quality may be RSRP or RSRQ or RSSI.
In this manner, the UE can select the SS block with the highest signal quality among the SS blocks whose contention-free preambles and/or resources are configured for the UE by the gNB.

Next, in operation 1802, the UE selects PRACH preambles and/or PRACH resources (or PRACH occasions) corresponding to the selected SS block, and in operation 1803, the UE selects the selection corresponding to the selected SS block. Msg1 is transmitted using the designated PRACH preamble and/or PRACH resource.

Once the SS block is associated with a dedicated preamble, the UE uses that PRACH preamble.
Otherwise, the UE randomly selects a PRACH preamble from the contention-based PRACH preambles corresponding to the selected SS block.

If the SS block is associated with a dedicated PRACH resource (or PRACH occasion), the UE selects the PRACH resource (or PRACH occasion) from the dedicated PRACH resource, otherwise the UE has a contention corresponding to the selected SS block. Select a PRACH resource (PRACH occasion) from the underlying PRACH resource (or PRACH occasion).
The UE selects the earliest available PRACH resource (or PRACH occasion) from the PRACH resources (or PRACH occasions) corresponding to the selected SS block (“dedicated” if available, otherwise “conflict”). ).
In one embodiment, the UE randomly selects one PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions) corresponding to the selected SS block ("dedicated" if available). , otherwise "conflict").
If multiple frequency division multiplexed PRACH resources (or PRACH occasions) are available within the time corresponding to the selected SS block, the UE can select the same frequency division multiplexed PRACH resource (or PRACH occasion) from the available multiple frequency division multiplexed PRACH resources (or PRACH occasions). Randomly select one PRACH resource (or PRACH occasion) with a probability of .
The UE randomly selects a PRACH preamble from the configured set of PRACH preambles with equal probability.

To calculate the power for transmitting the PRACH, the UE estimates the pathloss based on the signal received on the selected SS block.
After transmitting Msg1, at operation 1804, the UE determines whether the RAR corresponding to the Msg1 transmission (ie, Msg2) was successfully received.
If the UE successfully receives the RAR, then at operation 1805 there is no need to retransmit Msg1.
If the UE is unable to receive the RAR, then at operation 1806 the UE determines whether it has performed the maximum number of Msg1 transmissions allowed by the UE.
If the UE has not yet performed the maximum number of allowed Msg1 transmissions, the UE retransmits Msg1.
If the UE has performed the maximum number of allowed Msg1 transmissions, the UE will not retransmit Msg1.
During retransmission, at operation 1807, the UE determines whether the signal quality of the SS block previously selected for Msg1 transmission is greater than or equal to the threshold 'SSBlockThreshold'.
If the signal quality of the SS block previously selected for Msg1 transmission is greater than or equal to the threshold 'SSBlockThreshold', the UE will not reselect the SS block.
The threshold is set by the network in system information (e.g. with PRACH settings or in RMSI) or handover commands or dedicated RRC signaling.
The UE uses the same SS block that was selected for the previous transmission for PRACH preamble and/or PRACH resource selection and pathloss estimation for retransmission (ie, the next Msg1 transmission).
During retransmission, if the signal quality of the SS block previously selected for Msg1 transmission is less than the threshold 'SSBlockThreshold', the UE reselects the SS block at operation 1808 .
The UE selects the SS block with the highest signal quality among the SS blocks for the contention-free preamble and/or resources configured for the terminal by the gNB.

As an alternative embodiment of this method, CSI-RS can be used instead of SS blocks.
The UE selects the CSI-RS instead of the SS block using the same procedure as described above for the SS block.
The UE selects PRACH preambles and/or PRACH resources (or PRACH occasions) from the PRACH preambles and/or PRACH resources (or PRACH occasions) corresponding to the selected CSI-RS.

≪Method 15≫
Figure 19 is a flow chart illustrating UE operation for RACH transmission and retransmission based on method 15 according to embodiments of the present invention.

Referring to Figure 19, at operation 1901, the UE selects a suitable SS block for initial PRACH preamble transmission.
An SS block is suitable if the signal quality of the SS block is greater than a threshold 'SSBlockThreshold'.
In an embodiment, an SS block is suitable if the signal quality of the SS block is greater than or equal to a threshold 'SSBlockThreshold'.
'SSBlockThreshold' is set by the network in system information (e.g. with PRACH setting or in RMSI) or handover command or dedicated RRC signaling.
Signal quality is measured via resources of SS blocks carrying PSS and/or SSS and/or DMRS for PBCH.
Signal quality may be RSRP or RSRQ or RSSI.
If multiple SS blocks are suitable, the UE can select the SS block in one of the following schemes.

The UE selects the SS block with the highest signal quality among the suitable SS blocks.
The UE selects the SS block corresponding to the earliest available RACH resource (or PRACH occasion) in time among the suitable SS blocks.
The UE randomly selects one of the SS blocks with equal probability among the appropriate SS blocks.
The UE selects any SS block among the appropriate SS blocks.

The UE may select one of the following methods based on indications from the network (which may be signaled as part of PRACH configuration in SI and/or handover commands and/or dedicated RRC signaling).
That is, select the SS block with the highest signal quality among the appropriate SS blocks, or select the SS block corresponding to the earliest available RACH resource (or PRACH occasion) in time among the appropriate SS blocks. or randomly select one of the SS blocks with the same probability among the appropriate SS blocks.

The UE then selects PRACH preambles and/or PRACH resources (or PRACH occasions) corresponding to the selected SS block for transmitting the PRACH preamble (ie, Msg1).
At act 1902, the UE determines whether contention-free PRACH preambles and/or resources are configured for the selected SS block.
Once the UE is configured with a contention-free (i.e., dedicated) PRACH preamble and/or PRACH resource corresponding to the selected SS block, at operation 1903, the UE receives a dedicated PRACH preamble and/or PRACH resource corresponding to the selected block. Select a PRACH resource.
Otherwise, at operation 1904, the UE selects a PRACH preamble corresponding to the selected SS block and/or a PRACH preamble and/or a PRACH resource corresponding to the SS block selected from the contention-based subset of PRACH resources.

Once the SS block is associated with a dedicated preamble, the UE uses that PRACH preamble.
Otherwise, the UE randomly selects a PRACH preamble from the contention-based PRACH preambles corresponding to the selected SS block.

If the SS block is associated with a dedicated PRACH resource (or PRACH occasion), the UE selects the PRACH resource (or PRACH occasion) from the dedicated PRACH resource, otherwise the UE has a contention corresponding to the selected SS block. Select a PRACH resource (PRACH occasion) from the underlying PRACH resource (or PRACH occasion).
The UE selects the earliest available PRACH resource (or PRACH occasion) from the PRACH resources (or PRACH occasions) corresponding to the selected SS block (“dedicated” if available, otherwise “conflict”). ).
In an embodiment, the UE randomly selects one PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions) corresponding to the selected SS block (“dedicated” if available, otherwise "conflict").
If multiple frequency division multiplexed PRACH resources (or PRACH occasions) are available within the time corresponding to the selected SS block, the UE can select the same frequency division multiplexed PRACH resource (or PRACH occasion) from the available multiple frequency division multiplexed PRACH resources (or PRACH occasions). Randomly select one PRACH resource (or PRACH occasion) with a probability of .
The UE randomly selects a PRACH preamble from the configured set of PRACH preambles with equal probability.

At act 1905, the UE transmits Msg1 using the selected PRACH preamble and/or PRACH resources corresponding to the selected SS block.

To calculate the power for transmitting the PRACH, the UE estimates the pathloss based on the signal received on the selected SS block.
After transmitting Msg1, at operation 1906, the UE determines whether the RAR corresponding to the Msg1 transmission (ie, Msg2) was successfully received.
If the UE successfully receives the RAR, then in operation 1907 there is no need to retransmit Msg1.
If the UE is unable to receive the RAR, then at operation 1908 the UE determines whether it has performed the maximum number of Msg1 transmissions allowed by the UE.
If the UE has not yet performed the maximum number of allowed Msg1 transmissions, the UE retransmits Msg1.
If the UE has performed the maximum number of allowed Msg1 transmissions, the UE will not retransmit Msg1.
During retransmission, operation 1909 determines if the signal quality of the SS block previously selected for Msg1 transmission is greater than or equal to the threshold 'SSBlockThreshold'.
If the signal quality of the SS block previously selected for Msg1 transmission is greater than or equal to the threshold 'SSBlockThreshold', the UE will not reselect the SS block.
The threshold is set by the network in system information (e.g. with PRACH settings or in RMSI) or handover commands or dedicated RRC signaling.
The UE uses the same SS block that was selected for the previous transmission for PRACH preamble and/or PRACH resource selection and pathloss estimation for retransmission (ie, the next Msg1 transmission).
During retransmission, if the signal quality of the SS block previously selected for Msg1 transmission is less than the threshold 'SSBlockThreshold', the UE reselects the SS block at operation 1910 .
The UE selects an appropriate SS block.
If no suitable SS block is found, the UE reselects a suitable SS block during retransmission, as described below.

With the procedure described above, the UE may not be able to find any suitable SS block.
In this case, the UE either:

UE does not send Msg1.
Additionally, the UE triggers cell reselection for idle/inactive state and RLF (ie connection reconfiguration) for connected state.

The UE selects the SS block for which measurements are available or the SS block with the highest signal quality among all SS blocks.
In this case (i.e., when no suitable SS block is selected), during the retransmission of Msg1, the UE will receive , change the SS block.
In one embodiment, the UE is allowed to send Msg1 without selecting a suitable SS block for 'N' number.
Parameter N is either predefined or signaled by the network.

The UE delays Msg1 transmission until the UE finds a suitable SS block.
In one embodiment, the UE may delay the Msg1 transmission for a maximum time period 'T'.
The time period T is configured by the network in system information (e.g. with PRACH configuration or in RMSI) or handover commands or dedicated RRC signaling.
After this time expires, the UE triggers cell reselection for idle/inactive state and RLF for connected state (ie connection reconfiguration) if a suitable SS block is still not found.
Alternatively, if a suitable SS block is still not found, after this time has expired the UE has the highest signal quality among all SS blocks or among SS blocks for which measurements are available. Select SS block.

As an alternative embodiment of this method, CSI-RS can be used instead of SS blocks.
The UE selects the CSI-RS instead of the SS block using the same procedure as described above for the SS block.
The UE selects PRACH preambles and/or PRACH resources (or PRACH occasions) from the PRACH preambles and/or PRACH resources (or PRACH occasions) corresponding to the selected CSI-RS.

≪Method 16≫
FIG. 20 is a flow chart illustrating UE operation for RACH transmission and retransmission based on method 16 according to embodiments of the present invention.

Referring to Figure 20, at operation 2001, the UE selects a suitable SS block for initial PRACH preamble transmission.
An SS block is suitable if the signal quality of the SS block is greater than a threshold 'SSBlockThreshold'.
In an embodiment, an SS block is suitable if the signal quality of the SS block is greater than or equal to a threshold 'SSBlockThreshold'.
'SSBlockThreshold' is set by the network in system information (e.g. with PRACH setting or in RMSI) or handover command or dedicated RRC signaling.
Signal quality is measured over resources of SS blocks carrying PSS and/or SSS and/or DMRS for PBCH.
Signal quality may be RSRP or RSRQ or RSSI.

In operation 2002 of this method, the UE first checks whether there is a suitable SS block among the SS blocks for which dedicated PRACH preambles and/or PRACH resources are configured.
Once a suitable SS block for which dedicated PRACH preambles and/or PRACH resources are configured is found, the UE selects that SS block and assigns dedicated PRACH preambles and/or PRACH resources corresponding to the SS block selected in operation 2003. to select.
If multiple SS blocks are suitable SS blocks for which dedicated preambles and/or resources are configured, the UE may select the SS blocks in one of the following schemes.

The UE selects the SS block with the highest signal quality among the suitable SS blocks.
The UE selects the SS block corresponding to the earliest available RACH resource (or PRACH occasion) in time among the suitable SS blocks.
The UE randomly selects one of the SS blocks with equal probability among the appropriate SS blocks.
The UE selects any SS block among the appropriate SS blocks.

The UE may select one of the following methods based on indications from the network (which may be signaled as part of PRACH configuration in SI and/or handover commands and/or dedicated RRC signaling).
That is, select the SS block with the highest signal quality among the appropriate SS blocks, or select the SS block corresponding to the earliest available RACH resource (or PRACH occasion) in time among the appropriate SS blocks. or randomly select one of the SS blocks with the same probability among the appropriate SS blocks.

If no suitable SS block is found in the SS block in which the dedicated PRACH preamble and/or PRACH resources are configured, then in operation 2004 the UE selects a suitable SS block in the SS block in which the contention-based preamble and/or resources are configured. blocks, and in operation 2005 the UE selects contention-based PRACH preambles and/or PRACH resources corresponding to the selected SS blocks.
When multiple SS blocks are suitable SS blocks for which contention-based preambles and/or resources are configured, the UE may select the SS block in one of the following schemes.

The UE selects the SS block with the highest signal quality among the suitable SS blocks.
The UE selects the SS block corresponding to the earliest available RACH resource (or PRACH occasion) in time among the suitable SS blocks.
The UE randomly selects one of the SS blocks with equal probability among the appropriate SS blocks.
The UE selects any SS block among the appropriate SS blocks.

The UE may select one of the following methods based on indications from the network (which may be signaled as part of PRACH configuration in SI and/or handover commands and/or dedicated RRC signaling).
That is, select the SS block with the highest signal quality among the appropriate SS blocks, or select the SS block corresponding to the earliest available RACH resource (or PRACH occasion) in time among the appropriate SS blocks. or randomly select one of the SS blocks with the same probability among the appropriate SS blocks.

Next, at operation 2006, the UE transmits a PRACH preamble (ie, Msg1) using the selected PRACH preamble and/or PRACH resources corresponding to the selected SS block.

Once the SS block is associated with a dedicated preamble, the UE uses that PRACH preamble.
Otherwise, the UE randomly selects a PRACH preamble from the contention-based PRACH preambles corresponding to the selected SS block.

If the SS block is associated with a dedicated PRACH resource (or PRACH occasion), the UE selects the PRACH resource (or PRACH occasion) from the dedicated PRACH resource, otherwise the UE has a contention corresponding to the selected SS block. Select a PRACH resource (PRACH occasion) from the underlying PRACH resource (or PRACH occasion).
The UE selects the earliest available PRACH resource (or PRACH occasion) from the PRACH resources (or PRACH occasions) corresponding to the selected SS block (“dedicated” if available, otherwise “conflict”). ).
In an embodiment, the UE randomly selects one PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions) corresponding to the selected SS block (“dedicated” if available, otherwise "conflict").
If multiple frequency division multiplexed PRACH resources (or PRACH occasions) are available within the time corresponding to the selected SS block, the UE can select the same frequency division multiplexed PRACH resource (or PRACH occasion) from the available multiple frequency division multiplexed PRACH resources (or PRACH occasions). Randomly select one PRACH resource (or PRACH occasion) with a probability of .
The UE randomly selects a PRACH preamble from the configured set of PRACH preambles with equal probability.

To calculate the power for transmitting the PRACH, the UE estimates the pathloss based on the signal received on the selected SS block.
After transmitting Msg1, in operation 2007 the UE determines whether the RAR corresponding to the Msg1 transmission (ie Msg2) was successfully received.
If the UE successfully receives the RAR, in operation 2008 there is no need to retransmit Msg1.
If the UE is unable to receive the RAR, then in operation 2009 the UE determines whether it has performed the maximum number of Msg1 transmissions allowed by the UE.
If the UE has not yet performed the maximum number of allowed Msg1 transmissions, the UE retransmits Msg1.
If the UE has performed the maximum number of allowed Msg1 transmissions, the UE will not retransmit Msg1.
During retransmission, at operation 2010, the UE determines whether the signal quality of the SS block previously selected for Msg1 transmission is greater than or equal to the threshold 'SSBlockThreshold'.
If the signal quality of the SS block previously selected for Msg1 transmission is greater than or equal to the threshold 'SSBlockThreshold', the UE will not reselect the SS block.
The threshold is set by the network in system information (e.g. with PRACH settings or in RMSI) or handover commands or dedicated RRC signaling.
The UE uses the same SS block selected for the previous transmission for PRACH preamble and/or PRACH resource selection and path loss estimation for retransmission (ie, next Msg1 transmission).
During retransmission, if the signal quality of the SS block previously selected for Msg1 transmission is less than the threshold 'SSBlockThreshold', the UE reselects the SS block in operation 2011 .
The UE selects an appropriate SS block.
If no suitable SS block is found, the UE reselects a suitable SS block during retransmission as described below.

With the procedure described above, the UE may not be able to find any suitable SS block.
In this case, the UE either:

UE does not send Msg1.
Additionally, the UE triggers cell reselection for idle/inactive state and RLF (ie connection reconfiguration) for connected state.

The UE selects the SS block for which measurements are available or the SS block with the highest signal quality among all SS blocks.
In this case (i.e., when no suitable SS block is selected), during the retransmission of Msg1, the UE will receive , change the SS block.
In one embodiment, the UE is allowed to send Msg1 without selecting a suitable SS block between the 'N' number.
Parameter N is either predefined or signaled by the network.

The UE delays Msg1 transmission until it finds a suitable SS block.
In one embodiment, the UE may delay the Msg1 transmission for a maximum time period 'T'.
The time period T is set by the network in system information (e.g. with PRACH settings or in RMSI) or handover commands or dedicated RRC signaling.
After this time expires, the UE triggers cell reselection for idle/inactive state and RLF for connected state (ie, connection reconfiguration) if a suitable SS block is still not found.
Alternatively, if a suitable SS block is still not found, after this time has expired the UE has the highest signal quality among all SS blocks or among SS blocks for which measurements are available. Select SS block.

As an alternative embodiment of this method, CSI-RS can be used instead of SS blocks.
The UE selects the CSI-RS instead of the SS block using the same procedure as described above for the SS block.
The UE selects PRACH preambles and/or PRACH resources (or PRACH occasions) from the PRACH preambles and/or PRACH resources (or PRACH occasions) corresponding to the selected CSI-RS.

≪Method 17≫
Figure 21 is a flow chart illustrating UE operation for RACH transmission and retransmission based on method 17 according to embodiments of the present invention.

Referring to Figure 21, at operation 2101, the UE selects a suitable SS block for initial PRACH preamble transmission.
An SS block is suitable if the signal quality of the SS block is greater than a threshold 'SSBlockThreshold'.
In an embodiment, an SS block is suitable if the signal quality of the SS block is greater than or equal to a threshold 'SSBlockThreshold'.
'SSBlockThreshold' is set by the network in system information (e.g. with PRACH setting or in RMSI) or handover command or dedicated RRC signaling.
Signal quality is measured via resources of SS blocks carrying PSS and/or SSS and/or DMRS for PBCH.
Signal quality may be RSRP or RSRQ or RSSI.

In operation 2102 of this method, the UE first checks whether there is a suitable SS block among the SS blocks for which dedicated PRACH preambles and/or PRACH resources are configured.
Once a suitable SS block for which dedicated PRACH preambles and/or PRACH resources are configured is found, the UE selects that SS block and assigns dedicated PRACH preambles and/or PRACH resources corresponding to the SS block selected in operation 2103. to select.
If multiple SS blocks are suitable SS blocks for which dedicated preambles and/or resources are configured, the UE may select the SS blocks in one of the following schemes.

The UE selects the SS block with the highest signal quality among the suitable SS blocks.
The UE selects the SS block corresponding to the earliest available RACH resource (or PRACH occasion) in time among the suitable SS blocks.
The UE randomly selects one of the SS blocks with equal probability among the appropriate SS blocks.
The UE selects any SS block among the appropriate SS blocks.

The UE may select one of the following methods based on indications from the network (which may be signaled as part of PRACH configuration in SI and/or handover commands and/or dedicated RRC signaling).
That is, select the SS block with the highest signal quality among the appropriate SS blocks, or select the SS block corresponding to the earliest available RACH resource (or PRACH occasion) in time among the appropriate SS blocks. or randomly select one of the SS blocks with the same probability among the appropriate SS blocks.

If no suitable SS block is found among the SS blocks in which dedicated PRACH preambles and/or PRACH resources are configured, then in operation 2103 the UE selects the most suitable SS block among the SS blocks in which dedicated PRACH preambles and/or PRACH resources are configured. Select SS blocks with high signal quality and select dedicated PRACH preambles and/or PRACH resources corresponding to the selected SS blocks in act 2104 .

Then, at operation 2105, the UE transmits a PRACH preamble (ie, Msg1) using the selected PRACH preamble and/or PRACH resources corresponding to the selected SS block.

Once the SS block is associated with a dedicated preamble, the UE uses that PRACH preamble.
Otherwise, the UE randomly selects a PRACH preamble from the contention-based PRACH preambles corresponding to the selected SS block.

If the SS block is associated with a dedicated PRACH resource (or PRACH occasion), the UE selects the PRACH resource (or PRACH occasion) from the dedicated PRACH resource, otherwise the UE has a contention corresponding to the selected SS block. Select a PRACH resource (PRACH occasion) from the underlying PRACH resource (or PRACH occasion).
The UE selects the earliest available PRACH resource (or PRACH occasion) from the PRACH resources (or PRACH occasions) corresponding to the selected SS block (“dedicated” if available, otherwise “conflict”). ).
In an embodiment, the UE randomly selects one PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions) corresponding to the selected SS block (“dedicated” if available, otherwise "conflict").
If multiple frequency division multiplexed PRACH resources (or PRACH occasions) are available within the time corresponding to the selected SS block, the UE can select the same frequency division multiplexed PRACH resource (or PRACH occasion) from the available multiple frequency division multiplexed PRACH resources (or PRACH occasions). Randomly select one PRACH resource (or PRACH occasion) with a probability of .
The UE randomly selects a PRACH preamble from the configured set of PRACH preambles with equal probability.

To calculate the power for transmitting the PRACH, the UE estimates the pathloss based on the signal received on the selected SS block.
After transmitting Msg1, at operation 2106 the UE determines whether the RAR corresponding to the Msg1 transmission (ie, Msg2) was successfully received.
If the UE successfully receives the RAR, then in operation 2107 there is no need to retransmit Msg1.
If the UE is unable to receive the RAR, then at operation 2108 the UE determines whether it has performed the maximum number of Msg1 transmissions allowed by the UE.
If the UE has not yet performed the maximum number of allowed Msg1 transmissions, the UE retransmits Msg1.
If the UE has performed the maximum number of allowed Msg1 transmissions, the UE will not retransmit Msg1.
During retransmission, in operation 2109, the UE determines whether the signal quality of the SS block previously selected for Msg1 transmission is greater than or equal to the threshold 'SSBlockThreshold'.
If the signal quality of the SS block previously selected for Msg1 transmission is greater than or equal to the threshold 'SSBlockThreshold', the UE will not reselect the SS block.
The threshold is set by the network in system information (e.g. with PRACH settings or in RMSI) or handover commands or dedicated RRC signaling.
The UE uses the same SS block that was selected for the previous transmission for PRACH preamble and/or PRACH resource selection and pathloss estimation for retransmission (ie, the next Msg1 transmission).
During retransmission, if the signal quality of the SS block previously selected for Msg1 transmission is less than the threshold 'SSBlockThreshold', the UE reselects the SS block at operation 2110 .
The UE selects an appropriate SS block.
If no suitable SS block is found, the UE reselects a suitable SS block during retransmission.

As an alternative embodiment of this method, CSI-RS can be used instead of SS blocks.
The UE selects the CSI-RS instead of the SS block using the same procedure as described above for the SS block.
The UE selects PRACH preambles and/or PRACH resources (or PRACH occasions) from the PRACH preambles and/or PRACH resources (or PRACH occasions) corresponding to the selected CSI-RS.

The above procedures (Methods 1-17) can all be replaced in the CSI-RS case and the threshold signaled for the CSI-RS case can be used.
This is done for the CSI-RS based RACH proper handover case and beam recovery case.
Some procedures based on CSI-RS are described below, which, when performed using CSI-RS resources, have a fallback mechanism based on SS blocks where the RACH procedure fails or the maximum limit is reached.

≪Method 18≫
Figure 22 is a flow chart illustrating UE operation for RACH transmission and retransmission based on method 18 according to embodiments of the present invention.

Referring to FIG. 22, the UE selects an appropriate CSI-RS block for PRACH preamble transmission.
Such procedure is similar to the case of SS block based RACH.
When using CSI-RS, the procedure changes mentioned occur when the maximum retransmission limit for Msg1 is reached.
A fallback RACH procedure for the UE is then supported by the gNB to allow zero interruption time in handover scenarios.

First, the UE checks in operation 2207 whether the CFRACH procedure based on the target cell's SS block is supported.
If so, at operation 2208, perform one of the SS block based CF methods described above.
If not configured and indicated to the UE via the handover command, the UE shall perform the 'contention-based 4-step RACH procedure' based on the SS block of the target cell in operation 2209 .
Thus, the configuration is obtained by deciphering the SI of the target cell.
If the UE has to perform a contention-based RACH procedure, the UE can use methods 1-6 described above.
The same mechanism can be used when the UE finds that the CSI-RS measurements do not exceed the appropriate threshold level.

Continue to perform RACH in hope of success, otherwise fall back to SS-based RACH or UE triggers RLF for connected state (i.e. connection reconfiguration) .
For such a procedure, the key point to pay attention to is to select the CSI-RS block with the highest CSI-RS block RSRP among the CSI-RS blocks in which the CF resource is configured, and the same CSI-RS block is used for Msg1 (re)transmission during the CF random access procedure, and the selection of PRACH preambles and/or PRACH resources corresponding to the CSI-RS blocks selected from the CF resources configured for the UE is used the fact that it should be

In such a procedure, the UE selects a CSI-RS having the highest CSI-RS RSRP among appropriate CSI-RSs or CSI-RSs configured with CF resources in operation 2201, and the UE performs an operation At 2202, a dedicated PRACH preamble and/or PRACH resources corresponding to the selected CSI-RS are selected, and the UE selects the selected PRACH preamble and/or PRACH resources corresponding to the CSI-RS resources selected at operation 2203. is used to transmit the PRACH preamble (ie, Msg1).

When a CSI-RS resource is associated with a dedicated preamble, the UE uses that PRACH preamble.
Otherwise, the UE randomly selects a PRACH preamble from the entire pool of contention-based PRACH preambles or CF preambles corresponding to the selected CSI-RS resource.

If a CSI-RS resource is associated with a dedicated PRACH resource (or PRACH occasion), the UE selects a PRACH resource from this; otherwise, the UE selects a contention-based RACH resource ( Select PRACH resources (or PRACH occasions) from the entire pool of dedicated sets of resources (or PRACH occasions) intended for handover RACH.

After transmitting Msg1, in operation 2204 the UE determines whether the RAR corresponding to the Msg1 transmission (ie Msg2) was successfully received.
If the UE successfully receives the RAR, in operation 2205 it does not need to retransmit Msg1.
If the UE is unable to receive the RAR, then at operation 2206 the UE determines whether it has performed the maximum number of Msg1 transmissions allowed by the UE.
If the UE has not yet transmitted the maximum number of allowed Msg1 transmissions, the UE retransmits Msg1.
A fallback is required once the UE has performed the maximum number of allowed Msg1 transmissions.

If fallback is required, the UE transmits a PRACH preamble (ie, Msg1) with the selected PRACH preamble and/or PRACH resources corresponding to the selected SS block in operation 2208 or 2209.

Once the SS block is associated with a dedicated preamble, the UE uses that PRACH preamble.
Otherwise, the UE randomly selects a PRACH preamble from the contention-based PRACH preambles corresponding to the selected SS block.

When an SS block is associated with a dedicated PRACH resource (or PRACH occasion), the UE selects a PRACH resource (or PRACH occasion) from such subset, otherwise the UE corresponds to the selected SS block. Select PRACH resources (PRACH occasions) from contention-based PRACH resources (or PRACH occasions).
The UE selects the earliest available PRACH resource from the PRACH resources (or PRACH occasions) corresponding to the selected SS block (“dedicated” if available, otherwise “contention”).
In an embodiment, the UE randomly selects one PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions) corresponding to the selected SS block (“dedicated” if available, otherwise "conflict").
If multiple frequency division multiplexed PRACH resources (or PRACH occasions) are available within the time corresponding to the selected SS block, the UE can select the same frequency division multiplexed PRACH resource (or PRACH occasion) from the available multiple frequency division multiplexed PRACH resources (or PRACH occasions). Randomly select one PRACH resource (or PRACH occasion) with a probability of .
The UE randomly selects a PRACH preamble from the configured set of PRACH preambles with equal probability.

These resources for the SS block case can be either CF-based or CB-based depending on the decision taken by the UE.

≪Method 19≫
Figure 23 is a flow chart illustrating UE operation for RACH transmission and retransmission based on method 19 according to embodiments of the present invention.

Referring to FIG. 23, in operation 2301 the UE selects a suitable CSI-RS block for PRACH preamble transmission.
Such procedure is similar to the case of SS block based RACH.
The change in procedure mentioned occurs when the UE finds in action 2303 that no CF resources for the CSI-RS based RACH case are configured in the UE.
In such a case, the UE shall fall back to the SS-based RACH resource according to one of CF-based in operation 2304 or contention-based in operation 2305 .
The UE also uses such behavior when it finds that SS-based RACH resources are available first, as opposed to CSI-RS resources.
This can help the UE reduce access latency and minimize handover interruption time.

In such a procedure, the UE, in operation 2301, selects the CSI-RS with the highest CSI-RS RSPR among the reported CSI-RS measurements or the appropriate CSI-RS, and in operation 2302, the CF PRACH preamble and/or determine whether PRACH resources have been configured for the selected CSI-RS resources.
Once the UE is configured with a contention-free (i.e., dedicated) PRACH preamble and/or PRACH resource corresponding to the selected CSI-RS block, the UE, at operation 2306, sends the dedicated PRACH preamble and /or PRACH resources are selected, the UE transmits a PRACH preamble (ie, Msg1) using the selected PRACH preamble and/or PRACH resources corresponding to the selected CSI-RS resource in operation 2307 .

When a CSI-RS resource is associated with a dedicated preamble, the UE uses that PRACH preamble.
Otherwise, the UE randomly selects a PRACH preamble from the overall pool of contention-based PRACH preambles or CF preambles corresponding to the selected CSI-RS resource.

If a CSI-RS resource is associated with a dedicated PRACH resource (or PRACH occasion), the UE selects a PRACH resource from this; otherwise, the UE selects a contention-based RACH resource corresponding to the selected CSI-RS resource. (or PRACH occasion) or select PRACH resources (or PRACH occasions) from the entire pool of dedicated sets of resources (or PRACH occasions) intended for handover RACH.

After transmitting Msg1, at operation 2308, the UE determines whether the RAR corresponding to the Msg1 transmission (ie, Msg2) was successfully received.
If the UE successfully receives the RAR, in action 2309 it does not need to retransmit Msg1.
If the UE is unable to receive the RAR, then at operation 2310 the UE determines whether it has performed the maximum number of Msg1 transmissions allowed by the UE.
If the UE has not yet transmitted the maximum number of allowed Msg1 transmissions, the UE retransmits Msg1.
Once the UE has performed the maximum number of allowed Msg1 transmissions, the UE will not retransmit Msg1.

Fallback is required if the UE is not configured with contention-free (ie, dedicated) PRACH preambles and/or PRACH resources.
If fallback is required, the UE checks in operation 2303 if the CF RACH procedure based on the SS block of the target cell is supported, and the UE checks in operation 2304 or 2305 the selected SS block. transmit the PRACH preamble (ie, Msg1) using the selected PRACH preamble and/or PRACH resource corresponding to .

Once the SS block is associated with a dedicated preamble, the UE uses that PRACH preamble.
Otherwise, the UE randomly selects a PRACH preamble from the contention-based PRACH preambles corresponding to the selected SS block.

When an SS block is associated with a dedicated PRACH resource (or PRACH occasion), the UE selects a PRACH resource (or PRACH occasion) from such subset, otherwise the UE corresponds to the selected SS block. Select PRACH resources (PRACH occasions) from contention-based PRACH resources (or PRACH occasions).
The UE selects the earliest available time slot carrying resources from the PRACH resource (or PRACH occasion) corresponding to the selected SS block (“dedicated” if available, otherwise “contention”). .
In an embodiment, the UE randomly selects one PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions) corresponding to the selected SS block (“dedicated” if available, otherwise "conflict").
If multiple frequency division multiplexed PRACH resources (or PRACH occasions) are available within the time corresponding to the selected SS block, the UE can select the same frequency division multiplexed PRACH resource (or PRACH occasion) from the available multiple frequency division multiplexed PRACH resources (or PRACH occasions). Randomly select one PRACH resource (or PRACH occasion) with a probability of .
The UE randomly selects a PRACH preamble from the configured set of PRACH preambles with equal probability.

These resources for the SS block case can be either CF-based or CB-based depending on the decision taken by the UE.

≪Method 20≫
Figures 24A and 24B are flowcharts to illustrate UE operations for RACH transmission and retransmission based on method 20 according to embodiments of the present invention.

Referring to Figures 24A and 24B, at operation 2401, the UE selects a suitable CSI-RS block for PRACH preamble transmission.
Such procedure is similar to the case of SS block based RACH.
The change in procedure mentioned occurs when the UE attempts to perform a retransmission of the RACH preamble in action 2411 for the CF RACH or beam recovery based RACH case.
The UE performs CSI-RS resource reselection when the signal quality of the selected CSI-RS beam/resource is no longer deemed feasible in case of retransmission.
In other words, the UE may re-perform measurements on CSI-RS resources or rely on past measurements of other CSI-RS resources to be useful if one beam is blocked due to sudden environmental changes. can be done.
To calculate the power for transmitting the PRACH, the UE estimates the pathloss based on the signal received on the selected CSI-RS resource.

In such a procedure, the UE, in operation 2401, selects the CSI-RS with the highest CSI-RS RSPR among the reported CSI-RS measurements or the appropriate CSI-RS, and in operation 2402, the CF PRACH preamble and/or determine whether PRACH resources have been configured for the selected CSI-RS resources.
Once the UE is configured with a contention-free (i.e., dedicated) PRACH preamble and/or PRACH resources corresponding to the selected CSI-RS block, the UE, at operation 2406, sends the dedicated PRACH preamble and /or PRACH resources are selected, the UE, at operation 2407, transmits a PRACH preamble (ie, Msg1) using the selected PRACH preamble and/or PRACH resources corresponding to the selected CSI-RS resource.

When a CSI-RS resource is associated with a dedicated preamble, the UE uses that PRACH preamble.
Otherwise, the UE randomly selects a PRACH preamble from the overall pool of contention-based PRACH preambles or CF preambles corresponding to the selected CSI-RS resource.

If a CSI-RS resource is associated with a dedicated PRACH resource (or PRACH occasion), the UE selects a PRACH resource from this; otherwise, the UE selects a contention-based PRACH resource ( Select PRACH resources (or PRACH occasions) from the entire pool of dedicated sets of resources (or PRACH occasions) intended for handover RACH.

After transmitting Msg1, in operation 2408 the UE determines whether the RAR corresponding to the Msg1 transmission (ie Msg2) was successfully received.
If the UE successfully receives the RAR, in action 2409 it does not need to retransmit Msg1.
If the UE is unable to receive the RAR, then at operation 2410 the UE determines whether it has performed the maximum number of Msg1 transmissions allowed by the UE.
If the UE has not yet sent the maximum number of allowed Msg1 transmissions, the UE retransmits Msg1.
If the UE has performed the maximum number of allowed Msg1 transmissions, the UE will not retransmit Msg1.
During the retransmission, the UE determines in operation 2411 whether the signal quality of the CSI-RS block previously selected for Msg1 transmission is greater than or equal to the CSI-RS block threshold.
The UE does not reselect the CSI-RS block if the signal quality of the CSI-RS block previously selected for Msg1 transmission is greater than or equal to the threshold.
If the signal quality of the CSI-RS block previously selected for Msg1 transmission is less than the threshold, the UE at operation 2412 reselects the CSI-RS block.
The UE selects the CSI-RS block with the highest signal quality among all CSI-RS blocks transmitted by the gNB.
As another embodiment, the UE selects the CSI-RS block with the highest signal quality among all CSI-RS blocks that can be measured.

Fallback is required if the UE is not configured with contention-free (ie, dedicated) PRACH preambles and/or PRACH resources.
If fallback is required, the UE checks in operation 2403 whether the CF RACH procedure based on the SS block of the target cell is supported, and the UE checks in operation 2404 or 2405 whether the selected Send a PRACH preamble (ie, Msg1) using the selected PRACH preamble and/or PRACH resource corresponding to the SS block.

Once the SS block is associated with a dedicated preamble, the UE uses that PRACH preamble.
Otherwise, the UE randomly selects a PRACH preamble from the contention-based PRACH preambles corresponding to the selected SS block.

When an SS block is associated with a dedicated PRACH resource (or PRACH occasion), the UE selects a PRACH resource (or PRACH occasion) from such subset, otherwise the UE corresponds to the selected SS block. Select PRACH resources (PRACH occasions) from contention-based PRACH resources (or PRACH occasions).
The UE selects the earliest available time slot carrying PRACH resources from the PRACH resources (or PRACH occasions) corresponding to the selected SS block (“dedicated” if available, otherwise “contention”). ).
In an embodiment, the UE randomly selects one PRACH resource (or PRACH occasion) from the configured PRACH resources (or PRACH occasions) corresponding to the selected SS block (“dedicated” if available, otherwise "conflict").
If multiple frequency division multiplexed PRACH resources (or PRACH occasions) are available within the time corresponding to the selected SS block, the UE can select the same frequency division multiplexed PRACH resource (or PRACH occasion) from the available multiple frequency division multiplexed PRACH resources (or PRACH occasions). Randomly select one PRACH resource (or PRACH occasion) with a probability of .
The UE randomly selects a PRACH preamble from the configured set of PRACH preambles with equal probability.

These resources for the SS block case can be either CF-based or CB-based depending on the decision taken by the UE.

<<Multiple Msg1 transmissions before or while waiting for RAR for the first transmitted Msg1>>
Tx/Rx beam correspondence at the UE is maintained if at least one of the following is satisfied:

A UE determines a UE Tx beam for uplink transmission based on the UE's downlink measurements on one or more of the UE's Rx beams.
A UE determines a UE Rx beam for downlink reception based on indication of a transmit/receive point (TRP) based on uplink measurements on one or more Tx beams of the UE.
Tx/Rx beam support at the UE either maintains the UE capability or is independent of the UE capability.

For contention-free scenarios (eg handover), the UE is configured with a dedicated preamble.
If there is no TX/RX support at the UE, the UE has to send PRACH message 1 (i.e. dedicated PRACH preamble) using multiple UE TX beams as the UE does not know the specific UE TX beam. Yes, and future transmissions will be received by the gNB.

FIG. 25 shows an example where the UE performs Msg1 transmission only once before the RAR window.
Referring to FIG. 25, the UE transmits PRACH message 1 using UE TX beams in RACH transmission occasions and waits for RAR in the RAR window.
If no RAR is received, the UE transmits PRACH message 1 using other UE TX beams, such as in other RACH transmission occasions.
This may significantly delay access to the target cell.

Delay can be reduced by allowing the UE to transmit the PRACH preamble in one or more RACH transmission occasions before monitoring the RAR window.

26A and 26B are diagrams illustrating two examples in which multiple Msg1 transmissions are performed before the RAR window according to various embodiments of the present invention.
Referring to FIG. 26A, the UE transmits 'Msg.1' on the RACH transmission occasion configured in the frequency domain.
This is only possible if the UE has multiple antenna panels by using a single antenna panel and generating beams in only one direction.

Referring to FIG. 26B, the UE transmits 'Msg.1' on the RACH transmission occasion set in the time domain.
Without beam correspondence, the UE transmits "Msg.1" via different UL TX beams in different RACH TX occasions to access the target cell with less delay.

One of the issues in the above scenario is RAR monitoring (ie, is there a single RAR window or separate RAR windows for each transmitted Msg1).
It is proposed that the UE can monitor the RAR window to receive the RAR when the UE sends multiple Msg1 in one of the following schemes.
The number of Msg1 that the UE can send before or while monitoring the RAR window is configured by the network (eg, in system information or RRC signaling or handover commands).

≪Option 1≫
FIG. 27 is a diagram illustrating multiple Msg1 transmissions before or during RAR for the first transmitted Msg1 under Option 1 according to an embodiment of the present invention.

Referring to FIG. 27, the UE transmits the first Msg1 at Transmission Time Interval (TTI) 'X'.
Transmission occasions in which the UE can transmit the first Msg1 are indicated by the network.
The RAR window starts from TTI 'X+Offset', where the offset is predefined or set by the network (eg, in system information or RRC signaling or handover commands).
The offset should be "0".
The RAR window ends at TTI 'Z', where TTI 'Z' is the same as TTI 'X + offset + RAR window length', and the RAR window length is determined by the network (e.g., system information or RRC signaling).
From TTI 'X+1' to TTI 'Z-offset', the UE sends additional Msg1 in available PRACHTX occasions.
For each additional Msg1 sent by the UE, from TTI 'X+1' to TTI 'Z-offset', the UE will transmit the RAR window length ) to monitor the RAR.
The UE monitors the RAR corresponding to each transmitted Msg1 RA-RNTI and RAPID.
As soon as the UE receives the RAR for any Msg1 sent by the UE, it considers the RAR reception successful and does not send additional Msg1 in the interval TTI 'X+1' to TTI 'Z-offset'.

≪Option 2≫
28 and 29 are diagrams for explaining multiple Msg1 transmissions before or during RAR for the first transmitted Ms1 under Option 2 according to an embodiment of the present invention.

In this way, one or more sets of RACH TX occasions are configured by the network (eg in system information or RRC signaling or handover commands).
Each set consists of N TX occasions.
N is configurable by the network.
N may be set based on the number of TX beams at the UE that the UE can report to the gNB in capability signaling.
The TX occasions in each set may or may not be adjacent.
Each TX occasion set is associated with an SS block or CSI-RS to indicate a DL TX beam.
In case of such association, the SS Block ID or CSI-RS ID associated with each set is indicated by the network.
Alternatively, each TX occasion in the set is associated with an SS block or CSI-RS to indicate a DL TX beam in which one or multiple TX occasions can be associated with the same SS block or CSI-RS. .
Alternatively, TX occasions are not mapped to SS blocks or CSI-RS.
A UE may be assigned a preamble corresponding to an SS block or CSI-RS, and such assignment may be for some SS blocks or CSI-RS.

The UE sends Msg1 with a set of TX occasions.
The RAR window starts at an offset from the end of the set of RACH TX occasions as shown in FIG.

The UE monitors the RAR corresponding to each transmitted Msg1 RA-RNTI and RAPID in the RAR window.
As soon as the UE receives the RAR for any Msg1 sent by the UE, the UE shall consider this as successful reception of the RAR.
As an alternative embodiment, the RAR window starts at an offset from the end of the first RACH TX occasion in the set of RACH TX occasions as shown in FIG.

≪Option 3≫
FIG. 30 is a diagram illustrating multiple Msg1 transmissions before or during RAR for the first transmitted Msg1 under option 3 according to an embodiment of the present invention.

This method does not require special signaling such as the TX Occasion Indication for the first Msg1 as in Option 1 or the TX Occasion Set as in Option 2.
The PRACH resource is configured in the same manner whether or not the UE is allowed to transmit multiple Msg1.
In such a way for every Msg1 sent by the UE there is an independent RAR window.
For multiple Msg1s sent by the UE, the UE monitors the RAR with multiple RAR windows that the RAR windows can overlap.
The UE monitors the RAR corresponding to each transmitted Msg1 RA-RNTI and RAPID in the corresponding RAR window.
As soon as the UE receives the RAR for any Msg1 sent by the UE, the UE shall consider this as successful reception of the RAR.

<<Priority between Msg1 based on RRC Connection Request/Connection Resume Request and SI Request requested by UE in RRC Idle or Inactive state>>

〔scenario〕
The UE initiates SI acquisition on an on demand-basis.
Initiate a random access procedure (2-phase Msg1-based SI request or 4-phase Msg3-based SI request) to send the SI request.
The SI request procedure or random access procedure is completed when the UE receives an acknowledgment for the SI request sent by the UE (in Msg2 for Msg1-based SI requests and in Msg4 for Msg4-based SI requests). do.
After completing the SI request procedure, the UE monitors one or more SI windows for the requested SI message to receive the requested SI message.
During the time interval from initiation of the SI request to receipt of an acknowledgment for the SI request, the UE triggers a connection request/connection resume request.
Triggers may be due to location updates or RAN area updates or receiving paging or mobile originated calls, or for any other reason as specified in the specification.
Since the SI request procedure is in progress, connection setup may occur after the SI request procedure is completed.
However, this can delay connection setup.

In one embodiment of the invention, it is proposed that the UE prioritizes connection setup (ie connection request/connection resume request) via SI request.
The UE ends the ongoing SI request procedure and starts sending Connection Request/Connection Resume Request.
For Msg1 based SI requests, the ongoing random access procedure for sending SI requests is terminated.
A random access procedure for sending a Connection Request/Connection Resume Request is initiated by the UE.
For Msg3-based SI requests, the ongoing random access procedure for sending SI requests is not terminated.
Connection requests/connection resume requests are sent during the ongoing random access procedure.
SI requests are sent after connection setup.

In one implementation, RRC initiates transmission of SI requests.
While RRC waits for SI request acknowledgment from lower layer, RRC connection request/resume request is triggered (eg, based on indication from upper layer).
The UE's RRC notifies lower layers (ie MAC) to finish sending the SI request.
RRC sends RRC Connection Request/RRC Connection Resume Request to lower layers for transmission.
For Msg1-based SI requests, the MAC layer terminates ongoing RA procedures for Msg1-based SI requests based on indications from higher layers (ie, RRC).
In case of Msg3 based SI request, the MAC layer will continue the ongoing RA procedure and the connection request/connection resume request will be sent during the random access procedure.

In another embodiment of the invention, when an SI request is initiated to obtain one or more SIs that are either essential for connection setup or required for connection setup (e.g., access control parameters). , the UE is proposed to prioritize SI requests over RRC connection requests/resume requests.
The UE does not terminate ongoing SI requests.
If an SI request is initiated to acquire one or more SIs that are not mandatory or required for connection setup, the UE prioritizes the RRC connection request/resume request over the SI request.
The UE terminates the ongoing SI request and starts sending Connection Request/Connection Resume Request.
For Msg1-based SI requests, the ongoing random access procedure for sending SI requests terminates.
A random access procedure for sending a connection request/connection resume request is initiated by the UE.
For Msg3-based SI requests, the ongoing random access procedure for sending SI requests is not terminated.
Connection requests/connection resume requests are sent during the ongoing random access procedure.
SI requests are sent after connection setup.

In other embodiments of the invention, the connection setup is for one or more predefined access categories or the connection setup is for a specific access with a high priority (e.g. a priority greater than a specified value). category, or for one or more services defined in the specification where connection setup takes precedence over SI It is proposed to give priority to resume requests).
The UE terminates the ongoing SI request and starts sending Connection Request/Connection Resume Request.
For Msg1 based SI requests, the ongoing random access procedure for sending SI requests is terminated.
A random access procedure for sending a connection request/connection resume request is initiated by the UE.
For Msg3-based SI requests, the ongoing random access procedure for sending SI requests is not terminated.
Connection requests/connection resume requests are sent during the ongoing random access procedure.
SI requests are sent after connection setup.

In one embodiment of the invention, the network may indicate in the SI whether the UE should prioritize connection setup (ie connection request/connection resume request) over SI requests.

<<Distinction between Msg4 for connection request/connection resume request sent in Msg3 and Msg4 for SI request>>

〔scenario〕
After successful reception of RAR, UE sends Msg3 with UL acknowledgment received in RAR.
Msg3 contains a common control channel (CCCH) service data unit (SDU) (ie, system information request message).
A system information request message is generated by RRC.
Information about the SIBs used by the UE is included in the System Information Request message.
When UE1 and UE2 both send Msg1 using the same PRACH preamble and PRACH resource and receive the RAR, UE1 sends an SI request on Mgs3 and another RRC message (such as a connection request) on Msg3. Collisions may occur with other transmitting UEs 2 .
Msg3 from one of the UEs should be successful.
The gNB sends Msg4 in response to the received Msg3.
A Contention Resolution MAC Control Element (CE) carrying x bits (48 bits in LTE) of the CCCH SDU received in Msg3 is included in Msg4.
The transport block (TB) carrying the contention resolution MAC CE is scheduled by the PDCCH (physical downlink control channel) addressed to the T-CRNTI (temporary-cell radio network temporary identifier) (T-CRNTI is the gNB in the RAR). (note that it is first sent to the UE by ).
In a TB scheduled by PDCCH address in T-CRNTI, MAC layer at UE checks whether MAC PDU contains contention resolution MAC CE.
The X bit of the CCCH SDU in Msg3 for SI request and the X bit of the CCCH SDU in Msg3 for connection request (or other message) may be the same.
Therefore, there may be ambiguity when determining whether the received Msg4 corresponds to Msg3.

In one embodiment of the present invention, the SI request contains the UE identity (e.g., the international mobile subscriber identity (IMSI) or the system architecture evolution-temporary mobile subscriber identity (S-TMSI)) in addition to the information about the SIB used by the UE. or SUPI (subscriber permanent identifier) or any other UE identity defined in the system).
In the scenario described above, this means X bits of the CCCH SDU at Msg3 for the SI request sent by UE1 and X bits of the CCCH SDU at Msg3 for the connection request (or other message) sent by UE2. bits are not the same.
When the gNB receives Msg3 carrying the SI request from UE1, UE1 receives Msg4 and the content of the Contention Resolution MAC CE matches the x bits of the CCCH SDU sent by it in Msg3.
UE2 can also receive Msg4 (by the T-CRNTI being received by both UE1 and UE2), but the content of the contention resolution MAC CE is Msg3, with x bit does not match.
Once the gNB receives Msg3 carrying a connection request from UE2, UE2 receives Msg4 and the content of the Contention Resolution MAC CE matches the x bits of the CCCH SDU sent by it in Msg3.
UE1 may also receive Msg4, but the content of the Contention Resolution MAC CE will not match the x bits of the CCCH SDU sent by it in Msg3.

In an alternative embodiment of the invention it is proposed that the UE identity is not included in the system information request message.
Two types of MAC CE are defined for inclusion in Msg4.
One is for the case where Msg4 is sent in response to receiving Msg3 with SI request, and the other is for RMsg3 with a different message than SI request (e.g. connection request, connection resume request). For the case where Msg4 is sent in response to reception.
In one embodiment, the two MAC CEs have the same reserved Logical Channel Identifier (LCID) to be included in the MAC subheader of the MAC CE, and the type field is included in the content of the MAC CE. .
Such type field distinguishes whether such MAC CE responds to SI requests.
In other embodiments, separate LCIDs are reserved for each MAC CE.
One MAC CE is a contention resolution MAC CE and the other MAC CE is a SI ACK MAC CE.
Msg4 for Connection Request/Resume Request in Msg3 contains Conflict Resolution MAC CE.
Msg4 for SI request in Msg3 contains SI ACK MAC CE.
The Contention Resolution MAC CE contains the x bits of the CCCH SDU contained in Msg3.
The SI ACK MAC CE contains x bits of the CCCH SDU contained in Msg3.
Alternatively, the SI ACK MAC CE contains a list of one or more SIB types or SI message indices.
Alternatively, the SI ACK MAC CE contains a bitmap with each bit corresponding to an SIB or SI message.
For example, if the bitmap is 'b0b1b2b3b4', then the MSB 'b0' in the bitmap corresponds to the first SI message (or SIB type) in the list of SI messages (or SIB types) in SIB1, and bit 'b1' in the map corresponds to the second SI message (or SIB type) in the list of SI messages (or SIB types) in SIB1.
Alternatively, if the bitmap is 'b0b1b2b3b4', then the least significant bit (LSB) 'b4' in the bitmap is the first SI message (or SIB type) in the list of SI messages (or SIB types) in SIB1. and 'b3' in the bitmap corresponds to the second SI message (or SIB type) in the list of SI messages (or SIB types) in SIB1.
The bitmap length in MAC CE can be fixed.
Alternatively, the bitmap length in MAC CE may be variable.
The length may be the same as the number of SI messages (or SIB types) in the list of SI messages (or SIB types) in SIB1.

<<Preemption indication and DRX inactivity timer processing>>

〔scenario〕
The gNB schedules packets (DL or UL) by transmitting PDCCH.
During the duration of the DRX cycle, the gNB starts the inactivity timer (if it is not already running) or resets it (if the inactivity timer is already running).
In order to avoid collisions between URLL packets and eMBB packets, the gNB may skip (or suspend) the reception of scheduled DL packets or skip the transmission of scheduled UL packets by issuing preemption indications thereafter. Send to
The GNB may or may not schedule further interrupted packets thereafter.

In an embodiment of the present invention, when the UE receives a preemption indication to suspend scheduled packet transmission or reception, the UE receives the PDCCH scheduling the suspended packet, and if the inactivity timer is started. must abort the inactivity timer (if running).
In another embodiment of the present invention, when the UE receives a preemption indication to suspend scheduled packet transmission or reception, the UE starts an inactivity timer when it receives the PDCCH scheduling the suspended packet. , the inactivity timer (if running) shall be aborted if the elapsed time interval since the start of the timer is greater than or less than the threshold.
The threshold is either predefined or signaled by the network.

FIG. 31 is a block diagram showing a schematic configuration of a UE (user equipment) according to an embodiment of the present invention.
Referring to FIG. 31, the UE includes a transceiver 3110, a controller 3120 and a memory 3130.

Transceiver 3110, controller 3120, and memory 3130 are configured to perform the UE operations described above.
Although transceiver 3110, controller 3120, and memory 3130 are shown as separate entities, this could be implemented as a single entity, such as a single chip.
Transceiver 3110, controller 3120, and memory 3130 may be electrically connected and coupled to each other.

Transceiver 3110 transmits signals to and receives signals from other network entities, eg, BSs.

Controller 3120 controls the UE to perform functions according to one of the embodiments described above.
For example, the controller 3120 controls that the transceiver receives configuration information about RA resources associated with synchronization signal (SS) blocks from a base station (BS), and the transceiver receives one or more SS from the base station. controlling receiving blocks, determining whether there is at least one suitable SS block for which contention-free RA resources are configured among the one or more SS blocks based on the configuration information; selecting a suitable SS block for which contention-free RA resources are configured if there is at least one suitable SS block for which contention-free RA resources are configured in the SS block, and corresponding to the selected suitable SS block; A first RA preamble is selected, and the transceiver is configured to control transmission of the first RA preamble to the base station.
The controller 3120 is further configured to select a suitable SS block for which contention-based RA resources are configured if no suitable SS block for which contention-free RA resources are configured among the one or more SS blocks. be done.
Controller 3120 determines a particular SS block as a suitable SS block if the signal quality of the particular SS block among the one or more SS blocks is greater than a threshold set by radio resource control (RRC) signaling. configured as
Controller 3120 is further configured to select the next available time slot to carry RA resources from the RA resources corresponding to the selected SS block.
Controller 3120 is further configured for the transceiver to transmit a second RA preamble to the base station and monitor responses to the first RA preamble and the second RA preamble with a RAR window, where the RAR window is offset after transmission of the first RA preamble. Start later.
Controller 3120 may refer to a circuit, an ASIC, or at least one processor.

In embodiments, operations of the UE can be implemented using a memory 3130 that stores corresponding program codes.
Specifically, the UE is equipped with a memory 3130 to store program code that implements desired operations.
In order to perform the desired operations, the controller 3120 uses a processor or central processing unit (CPU) to read and execute program code stored in memory 3130 .

FIG. 32 is a block diagram showing a schematic configuration of a BS (base station) according to an embodiment of the present invention.
Referring to FIG. 32, the BS includes a transceiver 3210, controller 3220 and memory 3230. FIG.

The transceiver 3210, controller 3220, and memory 3230 are configured to perform the network (eg, gNB) operations described above.
Although transceiver 3210, controller 3220, and memory 3230 are shown as separate entities, they can be implemented as a single entity, such as a single chip.
Transceiver 3210, controller 3220, and memory 3230 may be electrically connected and coupled to each other.

A transceiver 3210 transmits signals to and receives signals from other network entities, eg, UEs.

Controller 3220 controls the BS to perform functions according to one of the embodiments described above.
For example, the controller 3220 controls the transceiver to transmit configuration information regarding RA resources associated with synchronization signal (SS) blocks to the terminal, and the transmitter to transmit one or more SS blocks to the terminal. and controlling the transceiver receiving the RA preamble from the terminal.
Controller 3220 may refer to a circuit, an ASIC, or at least one processor.

In embodiments, the operation of the BS is implemented using a memory 3230 that stores corresponding program code.
Specifically, the BS is equipped with a memory 3230 to store program code that implements desired operations.
To perform the desired operations, the controller 3220, by using a processor or CPU, reads and executes program code stored in the memory 3230.

While the invention has been shown and described with reference to such various embodiments, it will be readily apparent to those of ordinary skill in the art that the invention should not depart from the spirit and scope of the invention as defined by the appended claims and equivalents thereof. It will be understood that many changes in form and details may be made.

3110, 3210 transceiver 3120, 3220 controller 3130, 3230 memory

Claims (20)

A method performed by a terminal of a wireless communication system, comprising:
receiving contention-based random access (RA) configuration information and threshold information for selection of synchronization signal (SS) blocks (hereinafter, SS blocks) from a base station;
receiving contention-free RA configuration information and at least one RA preamble information associated with each of the SS blocks from the base station;
the configuration information of the contention-free RA includes information of contention-free RA resources associated with the SS block, having signal quality greater than the threshold within the SS blocks associated with the contention-free RA resources selecting a first SS block from among the at least one SS block associated with the contention-free RA resource, if at least one SS block is available;
selecting a first RA preamble corresponding to the selected first SS block based on the information of the at least one RA preamble associated with each of the SS blocks;
out of SS blocks associated with contention-based RA resources if the at least one block having signal quality greater than the threshold is not available in the SS blocks associated with the contention-free RA resources; selecting at least one SS block having a signal quality greater than the value;
selecting a second SS block from among the at least one SS block associated with the contention-based RA resource;
selecting a second RA preamble randomly with equal probability from among at least one competing RA preamble associated with the selected second SS block;
selecting a physical random access channel (PRACH) occurrence based on the selected first SS block or the selected second SS block;
and transmitting the first RA preamble or the second RA preamble on the selected PRACH occasion to the base station. The terminal method of claim 1, wherein the configuration information of the contention-based RA is included in an RRC (radio resource control) message. The terminal method of claim 1, wherein the signal quality greater than the threshold is identified based on reference signal received power (RSRP) of SS blocks. The terminal of claim 1, further comprising identifying a next available PRACH occurrence within PRACH occurrences corresponding to the selected first SS block or the selected second SS block. the method of. A method performed by a base station of a wireless communication system, comprising:
transmitting contention-based random access (RA) configuration information and threshold information for selection of a synchronization signal (SS) block (hereinafter, SS block) to a terminal;
transmitting contention-free RA configuration information and at least one RA preamble information associated with each of the SS blocks to the terminal;
receiving a first RA preamble or a second RA preamble from the terminal on a physical random access channel (PRACH) occurrence selected based on a first SS block or a second SS block;
at least the configuration information of the contention-free RA includes information of contention-free RA resources associated with the SS blocks, and having signal quality greater than the threshold within the SS blocks associated with the contention-free RA resources; if one SS block is available, the first SS block is selected from among the at least one SS block associated with the contention-free RA resource, and a first RA preamble corresponding to the selected first SS block is selected based on the information of the at least one RA preamble associated with the respective SS block;
if the at least one SS block having signal quality greater than the threshold is not available in the SS block associated with the contention-free RA resource, the threshold in the SS block associated with the contention-based RA resource; At least one SS block having signal quality greater than a value is identified, the second SS block is selected from among the at least one SS block associated with the contention-based RA resource, and the second RA preamble is selected from the selected randomly selected with equal probability from among at least one conflicting RA preamble associated with the second SS block. The method of claim 5, wherein the configuration information of the contention-based RA is included in an RRC (radio resource control) message. 6. The base station method of claim 5, wherein the signal quality greater than the threshold is identified based on reference signal received power (RSRP) of SS blocks. A terminal of a wireless communication system,
a transceiver;
connected to the transceiver;
Receives contention-based random access (RA) configuration information and threshold information for selection of synchronization signal (SS) blocks (hereinafter referred to as SS blocks) from a base station, and performs contention-free RA from the base station. configuration information and information of at least one RA preamble associated with each said SS block;
at least one in which the configuration information of the contention-free RA includes information of contention-free RA resources associated with an SS block, and having signal quality greater than the threshold within the SS blocks associated with the contention-free RA resources; selecting a first SS block from among the at least one SS block associated with the contention-free RA resource, if two SS blocks are available, to the information in the at least one RA preamble associated with each of the SS blocks; select a first RA preamble corresponding to the selected first SS block based on;
said threshold in an SS block associated with contention-based RA resources if said at least one SS block having signal quality greater than said threshold is not available in said SS block associated with said contention-free RA resource; identifying at least one SS block having a signal quality greater than; selecting a second SS block from among the at least one SS block associated with the contention-based RA resource; and associated with the selected second SS block. randomly selecting a second RA preamble from among at least one competing RA preamble with equal probability;
selecting a physical random access channel (PRACH) occurrence based on the selected first SS block or the selected second SS block;
and a controller that transmits the first RA preamble or the second RA preamble to the base station on the selected PRACH occasion. The terminal of claim 8, wherein the configuration information of the contention-based RA is included in an RRC (radio resource control) message. The terminal of claim 8, wherein the signal quality greater than the threshold is identified based on reference signal received power (RSRP) of SS blocks. The controller is further configured to identify a next available PRACH occasion among PRACH occasions corresponding to the selected first SS block or the selected second SS block. 9. The terminal according to item 8. A base station for a wireless communication system,
a transceiver;
connected to the transceiver;
Transmission of contention-based random access (RA) configuration information and threshold information for selection of a synchronization signal (SS) block (hereinafter referred to as SS block) to the terminal, and transmission of contention-free RA configuration information and transmitting information of at least one RA preamble associated with each of the SS blocks to the terminal;
a controller that receives a first RA preamble or a second RA preamble from the terminal on a physical random access channel (PRACH) occurrence selected based on the first SS block or the second SS block;
at least the configuration information of the contention-free RA includes information of contention-free RA resources associated with the SS blocks, and having signal quality greater than the threshold within the SS blocks associated with the contention-free RA resources; If one SS block is available, the first SS block is selected from among the at least one SS block associated with the contention-free RA resource, and a first RA preamble corresponding to the selected first SS block is each selected based on the information of the at least one RA preamble associated with the SS block of
within the SS block associated with the contention-based RA resource if the at least one SS block having signal quality greater than the threshold is not available in the SS block associated with the contention-free RA resource; At least one SS block having signal quality greater than a threshold is identified, the second SS block is selected from among the at least one SS block associated with the contention-based RA resource, and the second RA preamble is the A base station randomly selected with equal probability from among at least one conflicting RA preamble associated with the selected second SS block. The base station of claim 12, wherein the configuration information of the contention-based RA is included in an RRC (radio resource control) message. 13. The base station of claim 12, wherein the signal quality greater than the threshold is identified based on reference signal received power (RSRP) of SS blocks. determining whether a random access response (RAR) corresponding to the first RA preamble or the second RA preamble has not been received and whether the maximum number of RA preamble transmissions has been reached;
the RAR has not been received and the maximum number of RA preamble transmissions has not been reached, and the configuration information of the contention-free RA includes the information of the contention-free RA resource associated with the SS block; of the at least one SS block associated with the contention-free RA resource if the at least one SS block with signal quality greater than the threshold is available in the SS block associated with the contention-free RA resource; selecting a third SS block from within;
selecting a third RA preamble corresponding to the selected third SS block based on the information of the at least one RA preamble associated with each SS block;
selecting a PRACH occasion based on the selected third SS block or the selected third SS block;
The terminal method of claim 1, further comprising transmitting the third RA preamble on the selected PRACH occasion to the base station. said at least one said RAR has not been received, said maximum number of RA preamble transmissions has not been reached, and has a signal quality greater than said threshold within said SS block associated with said contention-free RA resource; identifying at least one SS block within the SS blocks associated with the contention-based RA resource that has a signal quality greater than the threshold if one block is not available;
selecting a fourth SS block from among the at least one SS block associated with the contention-based RA resource;
randomly selecting a fourth RA preamble with equal probability from among at least one competing RA preamble associated with the selected fourth SS block;
selecting a PRACH occasion based on the selected fourth SS block or the selected fourth SS block;
16. The terminal method of claim 15, further comprising transmitting the fourth RA preamble on the selected PRACH occasion to the base station. receiving a third RA preamble from the terminal on a PRACH occasion selected based on a third SS block,
The RAR (random access response) corresponding to the first RA preamble or the second RA preamble has not been received, the maximum number of RA preamble transmissions has not been reached, and the configuration information of the contention-free RA is the SS block. said third SS block containing information of an associated contention-free RA resource, if at least one SS block with signal quality greater than said threshold is available within said SS block associated with said contention-free RA resource; is selected from among the at least one SS block associated with the contention-free RA resource, and the third RA preamble corresponding to the selected third SS block is the at least one RA preamble associated with the respective SS block. receiving the third RA preamble , selected based on the information of
or
receiving a fourth RA preamble from the terminal on a PRACH occasion selected based on the fourth SS block,
The RAR corresponding to the first RA preamble or the second RA preamble has not been received, the maximum number of RA preamble transmissions has not been reached, and the threshold within the SS block associated with the contention-free RA resource. If the at least one SS block having signal quality greater than is not available, then at least one SS block having signal quality greater than the threshold is identified within SS blocks associated with the contention-based RA resource. , the fourth SS block is selected from among the at least one SS block associated with the contention-based RA resource, and the fourth RA preamble is from among at least one contention RA preamble associated with the selected fourth SS block. 6. The base station method of claim 5, further comprising receiving the fourth RA preamble that is randomly selected with equal probability. the controller determines whether a random access response (RAR) corresponding to the first RA preamble or the second RA preamble has not been received and whether the maximum number of RA preamble transmissions has been reached;
the RAR has not been received and the maximum number of RA preamble transmissions has not been reached, and the configuration information of the contention-free RA includes the information of the contention-free RA resource associated with the SS block; of the at least one SS block associated with the contention-free RA resource if the at least one SS block with signal quality greater than the threshold is available in the SS block associated with the contention-free RA resource; selecting a third SS block from within; selecting a third RA preamble corresponding to the selected third SS block based on the information of the at least one RA preamble associated with each of the SS blocks; 9. The method of claim 8, wherein a PRACH occasion is selected based on the selected 3rd SS block or the selected 3rd SS block, and the base station transmits the 3rd RA preamble in the selected PRACH occasion. terminal. The controller determines that the RAR has not been received, the maximum number of RA preamble transmissions has not been reached, and a signal quality greater than the threshold within the SS block associated with the contention-free RA resource. is not available, identifying at least one SS block having a signal quality greater than the threshold within an SS block associated with a contention-based RA resource; selecting a fourth SS block from among the at least one associated SS block and randomly selecting a fourth RA preamble from among at least one competing RA preamble associated with the selected fourth SS block with equal probability; 18. Selecting a PRACH occasion based on the selected fourth SS block or the selected fourth SS block, and transmitting the fourth RA preamble to the base station in the selected PRACH occasion. terminal described in . When the controller receives a third RA preamble from the terminal in a PRACH occasion selected based on the third SS block,
The RAR (random access response) corresponding to the first RA preamble or the second RA preamble has not been received, the maximum number of RA preamble transmissions has not been reached, and the configuration information of the contention-free RA is the SS block. said third SS block containing information of an associated contention-free RA resource, if at least one SS block with signal quality greater than said threshold is available within said SS block associated with said contention-free RA resource; is selected from among the at least one SS block associated with the contention-free RA resource, and the third RA preamble corresponding to the selected third SS block is the at least one RA preamble associated with each of the SS blocks. receiving the third RA preamble , selected based on the information of
or
When receiving a fourth RA preamble from the terminal in the PRACH occasion selected based on the fourth SS block,
the RAR corresponding to the first RA preamble or the second RA preamble has not been received, the maximum number of RA preamble transmissions has not been reached, and the threshold is within the SS block associated with the contention-free RA resource. If the at least one SS block with signal quality greater than the value is unavailable, then at least one SS block among SS blocks associated with the contention-based RA resource has signal quality greater than the threshold. identified, wherein the fourth SS block is selected from among the at least one SS block associated with the contention-based RA resource, and the fourth RA preamble is one of at least one contention RA preamble associated with the selected fourth SS block; 13. The base station of claim 12, receiving the fourth RA preamble that is randomly selected from among RA preambles with equal probability.

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